European Journal of Soil Science,2013doi:10.1111/ejss.12051 Microbial selenium transformations in seleniferous soils J.W.F e l l o w e s a,R.A.D.P a t t r i c k a,C.B o o t h m a n a,W.M.M.A l L a w a t i a,b,B.E.v a n D o n g e n a, J.M.C h a r n o c k a,J.R.L l o y d a&C.I.P e a r c e c
a School of Earth,Atmospheric and Environmental Sciences and Williamson Research Centre for Molecular Environmental Science, University of Manchester,Manchester,M139PL,UK,
b Higher College of Technology,Ministry of Manpower,Muscat113,Sultanate of Oman,and
c Paci?c Northwest National Laboratory,Richland,Washington99352,USA
Summary
Selenium(Se)is an essential trace element for animals and displays a narrow range between dietary de?ciency
and toxicity.The toxicity of Se depends on its bioavailability,which is directly related to its oxidation states,
of which four occur in the environment(Se VI,Se IV,Se0and Se II?).Microbial communities drive the cycling
of Se between these oxidation states.In order to investigate the effect of microbial activity on Se cycling in
the environment,a?eld site in County Meath,Ireland,was identi?ed with anomalously large concentrations
of Se as a result of weathering of black shales within the Lucan formation,leading to cases of Se toxicity
in farm animals.Soil cores were extracted from the site for Se speciation and microbial community analysis
prior to microcosm experiments to assess Se stability and microbial Se transformations.Selenium was present
as a recalcitrant,reduced organic phase that was strongly coordinated with carbon,concordant with suggested
hypotheses of Se phyto-concentration within a clay-lined,postglacial marshland.Selenium was not mobilized in
microcosm experiments,and supplementation with Se VI resulted in rapid reduction and removal from solution
as Se0.Additional electron donors did not affect Se stability or removal from solution,although nitrate did
hinder Se VI reduction.Terminal restriction fragment length polymorphism analysis indicated a signi?cant shift
in microbial community after amendment with Se VI.This work extends the current knowledge of Se cycling
in the environment,and provides information on the bioavailability of Se in the soil,which determines Se
content of foodstuffs.
Introduction
Selenium(Se)is an essential trace nutrient,present in a range of seleniferous proteins and enzymes but the small range between human dietary def?ciency(<40μg day?1)and toxicity(>400μg day?1)requires careful control,especially when monitoring human diets and supplementing feedstuffs for livestock (Fordyce,2007).The bioavailability to plants and,thus,toxicity of Se in crops is largely dependent on local geochemical conditions. In aqueous solution,such as groundwater and soil-pore waters, Se is commonly found as the Se IV and Se VI oxyanions,with the latter being predominant and mobile under more oxic,alkaline conditions(Oremland et al.,2004;Fordyce,2007;Lenz&Lens, 2009).Under reducing conditions,insoluble Se0and Se II?mineral phases are expected(Fordyce,2007;Lenz&Lens,2009).V olatile organic species,such as dimethylselenide,are also found in soils and contaminated ground and formed as a result of biotic
Correspondence:J.W.Fellowes.E-mail:Jonathan.Fellowes@ https://www.doczj.com/doc/df7592178.html,
Received15August2012;revised version accepted25February2013methylation(Lenz&Lens,2009).Biological transformations are a major driving force in the change of Se from one species to another,and a variety of biochemical mechanisms are responsible for the large range of seleniferous compounds found in the environment(Li et al.,2008;Lenz&Lens,2009).
Global soil Se concentrations are small,typically between0.1 and2.0μg g?1(Girling,1984;Berrow&Allan,1989),resulting in the need to amend Se-de?cient agricultural soils to increase dietary uptake(Broadley et al.,2006;Li et al.,2008).The underlying lithology largely determines the Se content of overlying soils (Fordyce,2007),and soils formed above Se-rich rocks such as black shales and coal measures,when coupled with evapo-or phyto-concentration mechanisms,can contain elevated Se concentrations in the mg g?1range(Fordyce,2007;Lenz&Lens, 2009).Accordingly,reports of Se toxicity in humans and livestock have been recorded in such areas(Crinion,1980;Rogers et al., 1990;Dhillon&Dhillon,1991;Fordyce et al.,2000).
Cases of Se toxicity in animals in Ireland date back to the late 19th century(Parle&Fleming,1983),and Rogers et al.(1990)list seven counties affected by large soil Se concentrations.Fleming (1962)identi?es a site near Trim,County Meath,with a soil Se
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concentration of1.2mg g?1.The origin of the Se is presumed to be the underlying interbedded muddy limestone/shales of the‘Calp Limestones’,part of the Dinantian Lucan Formation(Parle& Fleming,1983;McGrath&Fleming,2008).Weathering of these selenium-containing rocks by alkaline drainage waters favours the formation of mobile Se VI oxyanions,which are transported into localized low-lying,clay-lined basins,formed as a result of glaciation during the last ice age(Fleming,1962;Parle&Fleming, 1983;McGrath&Fleming,2008).Poor drainage results in the development of low-lying marshland,allowing Se to accumulate. In addition to its role as a nutrient,selenium is used in a wide range of chemical and technological applications because of its unique chemical and photo-optical properties,with a special current interest in nano-particles(Oremland et al.,2004;Lenz &Lens,2009;Pearce et al.,2009;Fellowes et al.,2011). Understanding the natural microbiological pathways developed to process large amounts of Se in the environment provides the opportunity to control its bioavailability and to synthesize selenium-based materials by an alternative,facile,‘green’route, including the production of novel bio-nano-materials(Oremland et al.,2004;Pearce et al.,2008,2009)
The aim of our work was to characterize the selenium in highly seleniferous soil(Fleming,1962)located in County Meath,Ireland,examining possible sources and enrichment mechanisms and the relationship between soil geochemistry and the incumbent microbial community.Testing the hypothesis that soil microorganisms are directly involved in the accumulation, concentration and remobilization of selenium will provide an increased understanding of geo-microbiological in?uences on selenium cycling in seleniferous environments.
Materials and methods
All chemicals used in this work were of analytical grade and supplied by Sigma Aldrich,Dorset,UK,unless otherwise stated. Field site and sampling techniques
The?eld site was identi?ed using data from Teasgasc(Fay et al., 2007)and published literature(Fleming,1962;Parle&Fleming, 1983;McGrath&Fleming,2008),which had revealed an area near Trim,County Meath,as having recorded soil Se concentrations exceeding1.2mg g?1at a depth of15–30cm,and reports of serious Se toxicity problems in cattle(Fleming,1962;Crinion, 1980).It is an area of subdued topography(range30m),and is a?at area at the bottom of a gentle slope.Following the identi?cation of a localized seleniferous soil by Fleming(1962), the exact location of the previously sampled seleniferous horizon was found and three soil cores were taken in close proximity using an Eijkelkamp(Giesbeek,the Netherlands)auger.The soil cores were approximately4cm in diameter and75cm long,the maximum attainable depth at this site.For comparison,a further three soil cores were taken approximately30m away,upslope of the?rst sampling site.The maximum attainable depth at this point was approximately50cm.Of the three cores taken at each site,two cores were stored aerobically for elemental and organic constituent analysis,whilst the third was collected and stored under anoxic conditions prior to microcosm and molecular ecology studies(see Supplementary Information for detailed sampling procedure). Soil core characterization
For mineralogical and chemical analyses,a soil core was dried at70?C and powdered.The mineral component of the soil core was then examined by X-ray diffraction(XRD)using a Bruker (Coventry,UK)D8Advance with a Cu kαsource(1.54?A). Aliquots of the soil powder were separated for loss on ignition (LOI)analysis to determine total organic carbon(C)content of the soils.Aliquots were also used to make wax-mounted pellets for X-ray?uorescence(XRF)analysis using a PANalytical(Almelo, The Netherlands)Axios Pw4400.
For lipid biomarker analyses the soils were freeze-dried, ground and extracted with a dichloromethane:methanol(2:1v/v) mixture in a soxhlet to obtain the total extractable lipids.These were fractionated into acid,apolar and polar fractions,using a combination of Agilent(Stockport,UK)Bond-Elut?and Al2O3 column chromatography,derivatized and analysed using an Agi-lent789A gas chromatograph coupled to an Agilent5975C MSD mass spectrometer(see Supplementary Information for details). X-ray absorption spectroscopy(XAS)was used to determine Se speciation in the anoxic soil cores,and undertaken on the high brilliance X-ray spectroscopy beamline ID26of the European Synchrotron Radiation Facility(ESRF),Grenoble, France.The storage ring was operated at a nominal6GeV with a current of100–200mA.The ID26beamline uses Si<111>monochromator crystals to deliver a spectral energy range of2.4–27keV,encompassing the Se K-edge at around 12.6keV.X-ray absorption near-edge structure(XANES)spectra were collected in?uorescence mode over the energy range 12.63to12.70keV.Standards were measured in transmission mode and comprised powdered red amorphous and trigonal elemental Se(Se0),iron selenide(FeSe2,Se II?),selenomethionine (C5H11NO2Se,Se II?),sodium selenite(Na2SeO3,Se IV)and sodium selenate(Na2SeO4,Se VI)(Figure1),which were all ground and diluted with boron nitride to optimize the edge jump. Soils and frozen aliquots from microcosms(described below) were mounted anoxically onto a multi-sample stage for XAS and measured with a liquid nitrogen cryostat,allowing for XAS determination of Se in both solid and liquid phases. Microcosm experiments
Microcosm experiments were undertaken to assess the role of microorganisms in the cycling of Se at the?eld site.One gram of anoxic soil from the seleniferous horizon(29–53cm)was added to30-ml serum bottles under an N2atmosphere.Ten millilitres of synthetic groundwater was added to each serum bottle.The synthetic groundwater was the same composition as groundwater
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Figure 1XANES pro?les for (top to bottom)(i)the Se standards,(ii)Co.Meath soil core,(iii)microcosms experiments and (iv)Se VI -amended microcosm experiments.Edge energies for Se 0(12.654keV)and Se VI (12.662keV)are highlighted (dashed lines).
samples taken at the ?eld site and analysed by ion chromatography (IC)using a Thermo Scienti?c (Hemel Hempstead,UK)Dionex DX600,and contained 29.8m m sodium bicarbonate, 1.34m m potassium chloride and 0.83m m magnesium sulphate at pH 7.5.The microcosms were incubated at 20?C under the following conditions:(i)oxic (the rubber stoppers were penetrated with needles ?tted with 0.22-μm ?lters and the headspace was replaced with two volumes of ?lter-sterilized air every 2days),(ii)anoxic,(iii)anoxic plus sodium acetate (10m m )and (iv)anoxic plus sodium acetate (10m m )and sodium nitrate (10m m ).All microcosms were repeated in triplicate,and autoclaved controls for each condition tested were prepared and analysed.A second set of microcosms were prepared as described earlier and amended with 5m m sodium selenate.
Prior to sampling,the bottles were shaken and samples of the soil suspension were taken at 7-day intervals with aliquots ?ash frozen in liquid N 2and stored at ?80?C for XAS.A second aliquot (1ml)was removed,centrifuged (12470g ,5minutes)and the supernatants analysed by IC with a Thermo Scienti?c (Hemel Hempstead,UK)Dionex DX600and ICP-AES with a Perkin Elmer (Waltham,Massachusetts,USA)Optima 5300.A third aliquot (0.5ml)was removed and digested in 0.5m HCl (4.5ml)for 1hour for ferrozine analysis to determine ferrous iron,followed by subsequent digestion with 200μl hydroxylamine (6.26m )for 1hour and ferrozine analysis to determine total iron (Lovley &Phillips,1988).
Microbial ecology
Aliquots of the microcosms were taken at each sample point for molecular ecology analysis.Samples were removed using sterile anaerobic microbiological techniques and ?ash frozen in liquid N 2in 1.5ml Eppendorf (Stevenage,UK)tubes prior to storage at ?80?C.DNA was extracted from 200μl sediment slurry using a PowerSoil DNA Isolation Kit (MO BIO Laboratories,Solana Beach,CA,USA).
The 16S rRNA gene region of each sample was ampli?ed in triplicate by PCR using ?uorescently labelled primers and puri?ed prior to further use (see Supplementary Information for further details).
Using manufacturer-recommended protocols,150ng μl ?1of sample DNA was used for restriction digestion with enzymes Hha I and Msp I (New England Biolabs,Ipswich,MA,USA)in separate reactions.Size determination of T-RFs was performed using a LIZ 1200size standard (Applied Biosystems,Warrington,UK)and an ABI (Paisley,UK)Prism 3100Genetic Analyser and Peak Scanner software.Peaks recorded at less than 50bp in length were discarded.Duplicate data outputs allowed for the alignment of T-RF peaks and removal of erroneous data using T-Align (Smith et al .,2005),assuming a standard con?dence interval of https://www.doczj.com/doc/df7592178.html,parison results ?les generated by T-Align for each enzyme digest were then transferred into PAST (Hammer et al .,2001)statistical software for multivariate cluster analysis judging compositional dissimilarity between sample sites using the Bray-Curtis dissimilarity measure.
Results and discussion Se in the soil components
Examination of the soil cores revealed that the soil comprised a top layer of ?ne grained brown soil to a depth of 29cm,below which was a 13-cm band of loosely consolidated,dry,dark brown/black soil,composed of degraded plant fragments.Underlying this was a series of interbedded layers of brown soil and grey-blue clay (Figure 2).The XRD analysis of this soil core showed that quartz was the dominant mineral throughout the core with minor amounts of calcite,illite and albite.
The XRF results from the soil core (Figure 2,Table S1)show that Se was enriched when compared with the average global soil content of less than 2μg g ?1(Girling,1984;Berrow &Allan,1989),throughout the pro?le,with values ranging from 14.5to 156.2μg g ?1.The largest Se concentrations occurred between 29and 53cm,and peaked between 29and 43cm (Figure 2).The total organic carbon content of the soil core ranged between 10.5and 33.8%(dry mass basis).
Several strong correlations with Se were observed in the XRF analyses,including positive correlations with total organic C,sulphur and a range of toxic heavy metals,including copper,cadmium and uranium (see Supplementary Information Table S2for correlation statistics).No correlation was seen between Se and molybdenum (Mo),despite large Se and Mo concentrations in
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Figure2Variations in the Se,C,SiO2and lipid biomarkers throughout the soil core.Dashed lines represent suggested boundaries of the horizons.A strong positive correlation is observed between Se and total organic C,whilst a strong negative correlation exists with SiO2.Correlations are noted between Se and HMW n-alkanes,HMW n-alkanoic acids,HMW n-alkanols,LMW n-alkanoic acids and LMW n-alkanols.
the underlying‘source’rocks(Parle&Fleming,1983).Negative correlations are observed with the common rock forming elements silicon,aluminium and potassium.
The soil pro?le taken upslope from the boggy area revealed a thinner,well-drained soil(about50cm deep)with a dis-turbed top layer that progressed into a clay-rich lower pro-?le.Elemental analysis of this soil core had a much smaller Se(3.4μg g?1maximum)and total organic C(6.7%by mass) concentrations.
The XANES spectra of the Se standards(Figure1)showed that the K-edge absorption energy increased with oxidation state:12.6535and12.6540keV for the reduced Se phases Se II?and Se0,respectively,12.6555keV for organic phases such as selenomethionine,12.6584keV for Se IV and12.6615keV for Se VI.The XANES pro?les for the soil cores(Figure1)showed differences in the Se absorption edge energy and in the post-edge structure demonstrating that Se species vary through the soil pro?le.The Se species in the top of the pro?le(0–10cm depth,38.3μg g?1Se)had an absorption edge at12654.1eV, similar to the edge energy of inorganic Se0(Figure1),although differences in the post-edge structure to the Se0standard indicate that a reduced,organic Se phase was present.The XANES data show that the Se found in the lower,interbedded clay part of the pro?le is of the same form as that at the surface(Figure1). However,analysis of the highly seleniferous horizon(156.2μg g?1 Se at29–43-cm depth)showed an absorption edge energy of 12655.2eV,1.1eV greater than for the top and bottom horizons. This absorption energy closely matched that seen for Se bonded to methyl groups in the reduced organic Se phase selenomethionine (Figure1),although differences in the post-edge structure are also visible.
The strong correlation between Se and total organic C indicates an association of Se with organic matter,and so organic biomarker analysis was undertaken.The lipid composition was analysed by GC-MS and both low(LMW,
The XRF and organic analyses de?ned three distinct geochemi-cal horizons(Figure2):(i)an upper most horizon extending from the surface down to29cm,consistent with recent agricultural disturbance and mixing of the O and A horizons;(ii)an organic-rich soil between29and53cm with an extensive component of higher plant matter,which contained elevated C,Se and heavy metal concentrations;and(iii)a lower,clay-rich layer extending below53cm,indicating the presence of a small lake deposit as proposed by Parle&Fleming(1983)and providing an imperme-able base to the pro?le.This is consistent with the topography of the site,where the low-lying area drains the surroundings and has slowly become in?lled.
The lowest layer analysed(70–75cm)had the smallest Se concentration of14.5μg g?1,still considerably larger than the 0.1–2μg g?1global average Se soil concentration(Girling,1984;
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Table 1Lipid biomarker variations throughout the soil pro?le.
Depth /cm
CPI 21-31a CPI 20-30a CPI 20-30a C 23:C 25
n -alkane C 23:C 29n -alkane
P aq b ACL 25-33c Alkanes
FA d Alkanols 0–109.3 3.626.20.460.180.1829.410–207.2 4.233.00.470.190.2329.020–29 6.7 4.743.10.400.160.2128.829–43 5.5 2.78.30.740.250.2328.643–53 6.2 3.322.40.500.170.1629.653–628.6 4.255.60.530.180.1429.662–70 6.1
0.27
28
0.48
0.17
0.17
29.5
a To express the n -alkane odd-over-even predominance of the high molecular
weight (HMW)hydrocarbons,carbon preference index (CPI)is used,which can be calculated using the following equation (van Dongen et al .,2008):
CPI =1/2 (Xi +Xi +2+---+Xn )/ (Xi -1+Xi +1+---+Xn -1)+1/2
(Xi +Xi +2+
---+Xn )/
(Xi +1+Xi +3+---+Xn +1).
b P aq =(C 23+25)/(C 23+C 25+C 29+C 31)(Ficken et al .,2000;Nichols et al .,2006;Zhou et al .,2010).
c Average chain length (Jeng,2006),ACL i-n = ([i ·X i ]+[i +2·X
i +2]+...+[n ·X n ])/
(X i +X i +2+...+X n ).
d Fatty acids,n -alkanoic acids.
Berrow &Allan,1989).The dominance of quartz and limited carbonate throughout the seleniferous soil pro?le alongside the presence of an impermeable clay base suggests that the soil has been developed on reworked sediment,rather than directly on the interbedded limestones and mudstones of the underlying Lucan Formation.This is further supported by the decreasing Se concentration with increasing depth below the reworked horizon,a trend opposite to that expected if the Se was originating from the directly underlying bedrock.
Large concentrations of Se (156.2μg g ?1)were found within a narrow,carbon-rich (33.8%by mass total organic C)horizon between 29and 43cm.This band also contained elevated concentrations of heavy metals (Table S1)and HMW and LMW n -alkanes,n -alkanoic acids and n -alkanols (Figure 2),indicative of signi?cant contributions from higher plant and bacterial matter.Selenium content was strongly correlated throughout the soil pro?le with total organic C:the XANES analysis precludes the presence of inorganic Se (Figure 1)in this carbon-rich horizon.The absorption edge energy and structure are similar to those seen for the organic Se phase selenomethionine.Published XANES results (Ryser et al .,2005)for a number of organo-selenium compounds show how the edge energy and structure can vary between otherwise very similar compounds,because of the degree of covalency in organic Se II ?phases.Therefore the Se within this horizon was probably a reduced organo-selenium form similar to selenomethionine.
The ?eld,XRF,organic and XANES ?ndings are consistent with those expected for the concentration of Se in a small,low-lying fen,which formed as a result of the in?lling of a small postglacial lake,which was fed by drainage of the surrounding area directly overlying seleniferous components of the Lucan Formation,as proposed previously (Fleming,1962;Parle &Fleming,1983;McGrath &Fleming,2008).This is supported by the much smaller Se concentrations reported in the soil core taken
uphill,suggesting downhill movement of percolating,Se-bearing drainage waters.The strong correlation between total organic C and Se,and the large higher plant remains as indicated both by lipid biomarker analysis and observations of plant material within the seleniferous horizon,suggests that phyto-concentration was the mechanism by which Se accumulated.The lipid biomarkers are dominated by C 27,C 29and C 31,consistent with signi?cant terrestrial higher plant input,and probably originating from the epicuticular waxes of vascular plants (V onk &Gustafsson,2009;Zhou et al .,2010).
The increase in the C 23:C 29ratio (Table 1),the medium molecular weight lipid biomarkers typically associated with Sphagnum species compared with the higher molecular weight lipids of terrestrial vascular plants (Nichols et al .,2006;Zhou et al .,2010),indicates that Sphagnum species were more prevalent during the deposition of the seleniferous horizon.Calculated P aq values between 0.1and 0.4support these ?ndings (Table 1)(Ficken et al .,2000;Nichols et al .,2006;Zhou et al .,2010).The lipid biomarkers also allow for a relative palaeoclimatic reconstruction at the time of deposition based upon the varying ratios of the organic materials.Elevated P aq values and a noticeable increase in the ratios of the C 23:C 25and the C 23:C 29n -alkanes (Table 1)are indicative of a wetter climate at the time of deposition of the seleniferous horizon relative to the horizons above and below (Ficken et al .,2000;Nichols et al .,2006;V onk &Gustafsson,2009;Zhou et al .,2010).There is also an appreciable decrease in the n -alkane average chain length (ACL)from the lower horizon to the seleniferous horizon,suggesting a transition to a cooler climate during the deposition of the seleniferous organics.Rapid deposition and burial under these conditions would help to preserve the Se-enriched plant matter as the peat-like material found,hindering microbial activity and the release of Se.
Uptake and enrichment of Se by higher plants has been noted previously;the location within the plant is largely dependent on species,with Se possibly located within leaves,stems,rhizomes and/or roots as a range of organic Se compounds,Se-amino acids,selenoproteins and their biochemical precursors,including Se-methylSec,methylselenol,selenocysteine and selenomethionine (Banuelos &Lin,2005;Broadley et al .,2006;Li et al .,2008;Pilon-Smits &Leduc,2009).
Variations seen in the XANES pro?le of the soil core indicate that Se is found as a distinct form within the highly seleniferous horizon compared with those above and below (Figure 1),and represents upper and lower boundaries for Se phyto-concentration within the site.
The role of bacteria in the concentration of Se at this site can also be examined.As noted,positive correlations exist between the LMW (probably bacterial)lipids and Se (Figure 2),and analysis of the n -alkanol biomarkers implies a signi?cant input of LMW organics at the seleniferous horizon (Figure 2).These ?ndings contradict those reported for the n -alkanes,which suggest that higher plant materials https://www.doczj.com/doc/df7592178.html,rge proportions of C 16n -alkanoic acids are found within the soil pro?le,consistent
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Figure 3Soil microcosm geochemical data.Key to symbols:(solid lines)extractable Fe II ,(dashed line)NO 3?;(squares)oxic,(circles)anoxic,(triangles)anoxic and acetate,(diamonds)anoxic,acetate and nitrate.Error bars omitted for clarity;average errors (as percentage)are <20%for Fe II and <8%for NO 3?.
with microbial reworking of the organic sediments (Zhou et al .,2010).As n -alkanols and n -alkanoic acids are amongst the least recalcitrant lipids to bacterial degradation,it is likely that the correlation seen between the LMW components and the Se results from increased bacterial activity within the seleniferous horizon,stimulated by substantial amounts of organic material.There is no indication that the increased Se concentration is directly attributable to the microbial activity within this layer.
Microcosm experiments
Microcosms without additional Se.Signi?cant amounts of
Fe II were observed in microcosm solutions after one week of incubation at 20?C in all of the conditions tested,with the exception of sterilized controls (Figure 3).Large initial rates of Fe III reduction occurred in anoxic microcosms,with slurry-extracted Fe II concentrations of about 30m m after four weeks incubation.Fe III reduction rates were comparable in soils both with and without additional electron donor (sodium acetate,10m m ).The addition of 10m m nitrate to the microcosms resulted in rapid denitri?cation,with all nitrate being removed in less than 1week (Figure 3).A decrease in the rate and extent of Fe III reduction was observed with the addition of 10m m nitrate.
The microcosms were sampled at weeks 0,2and 4for XAS analyses (Figure 1),which showed that the Se K-edge absorption energy at 12655.2eV did not change throughout the course of the experiment.
The formation of Fe II in the microcosms,driven by anoxic dis-similatory iron-reducing bacteria,was supported by the oxidation of the large organic content of the samples.Addition of 10m m acetate as an extra electron donor for Fe III reduction therefore had little impact.The simultaneous addition of nitrate to the micro-cosms provided an alternative electron acceptor,thus decreasing
the rate of Fe III reduction.Detectable Fe II in solution in the oxic microcosms suggested that microbial activity,coupled with a large concentration of organic material,led to depleted oxygen con-centrations within these microcosms and reduction of Fe III by anaerobic microbial metabolism.
Despite the large rates of microbial activity recorded in these soils,under both oxic and anoxic conditions,the reduced organic Se phase did not change or enter the mobile aqueous phase,indicating that the organic Se phase was resistant to changing geochemical conditions and microbial activity over a period of 4weeks.
Se VI -amended microcosms.Microcosms were amended with
5m m Se VI to assess the cycling of bioavailable Se oxyanions in these naturally seleniferous soils.No Fe III reduction or Se VI reduction was observed in the autoclaved control microcosms,indicating that the changes measured result from microbial activity.As with the unamended microcosms,small concentrations of Fe II were measured in solution in the solids incubated under oxic conditions,indicating that microbial activity,even in the presence of large Se VI concentrations,was suf?cient to deplete the oxygen concentrations to the extent where Fe III reduction could take place (Figure 4).Reduction of Se VI was also measured in the oxic microcosms at 50μm day ?1,with 67%remaining in solution after four weeks.The reduction of Se VI proceeded via Se IV ,with 0.5m m measurable in solution after four weeks (Figure 4).The rate of Se reduction was much faster in the anoxic microcosms,with 100%of the Se VI being removed from solution within one week.Se IV (0.8m m )was measured in solution after one week at 20?C,but was completely removed from solution after two weeks.Reduction of Fe III also occurred under anoxic conditions in the presence of Se VI ,with a steady increase in concentration in slurry-extracted Fe II of 52μm hour ?1over the four-week period.The initial Fe III reduction rate in the presence of Se VI was half that measured in the unamended microcosms,but the total extractable Fe II was the same both in the presence and absence of Se VI after incubation for four weeks.No signi?cant change in the rate of Fe III or Se VI reduction upon addition of acetate (10m m )was observed in the Se VI -amended microcosms,con?rming that the organic-rich,seleniferous soil horizons were not limited by a lack of electron donors.Rapid denitri?cation occurred in the Se VI -amended microcosms with acetate and nitrate,and all nitrate was removed from solution within one week.In these Se-amended microcosms,the rate of Fe III reduction in the presence of nitrate was reduced by 27%compared with when it was absent.All amended Se was removed from solution after three weeks incubation,rather than after two weeks in the absence of 10m m nitrate.Both Se VI (0.9m m )and Se IV (2.4m m )were measurable after one week and Se IV (0.4mM)was still measurable after two weeks.
The Se-amended microcosms were sampled at weeks zero,two and four for XAS analyses (Figure 1).The XANES for the start of the experiment are consistent with the presence of Se VI .Comparison of the XANES of the Se VI -amended microcosms with
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Figure4Geochemical data for Se VI-amended microcosms.(a)oxic microcosms,(b)anoxic microcosms,(c)anoxic and acetate,(d)anoxic,acetate and nitrate.Key to symbols:(solid squares)Fe II,(open circles)Se VI,(open triangles)Se IV,(open squares)NO3?.Error bars omitted for clarity;average errors (as percentage)are18%for Fe II,<8%for Se VI,7%for NO3?and<39%for Se IV,because of proximity to lower detection limit for this species.
those for a range of Se standards(Figure1)shows that the Se was reduced from Se VI(edge energy12661.5eV)to insoluble Se0(12654.0eV)by week two.No intermediate Se IV phase was detected in the XANES data.The XANES pro?les for the oxic microcosms showed increasing proportions of Se IV and Se0with a decreasing Se VI intensity over four weeks,as Se reduction took place.After four weeks incubation under oxic conditions, the XANES pro?le provided no evidence for the presence of Se VI;however,2.9m m Se VI was detected by IC,highlighting the necessity for complementary analytical techniques for complex environmental samples containing both solid and aqueous phases. The Se concentration of the amended microcosms was also suf?cient to collect EXAFS data of the solid Se phase present after four weeks.Theoretical?tting of the EXAFS oscillations and resultant Fourier transforms(Figure5)indicate an inner shell of two Se scatterers at0.24nm with a second outer shell of two Se atoms at0.33nm.These?ndings are consistent with red,elemental α-Se(Pearce et al.,2008)and con?rm the presence of this phase in the microcosms.
Microbial community analysis.Bray Curtis dissimilarity analy-sis(Figure6,Supplementary Figures S1–3)shows that the micro-bial community remained largely unchanged after four weeks incu-bation at20?C under anoxic conditions,indicating that the selenif-erous,organic-rich horizon contains a community that was stable.The Terminal restriction fragment length polymorphism analysis (TRFLP)results for the initial microbial community and for the community after four weeks incubation with or without10m m nitrate remain similar(60–65%similarity),inferring that a sig-ni?cant component of the extant community was probably able to respire by using nitrate.These?ndings are consistent with the agricultural use of the land,where nitrate addition in fertilizers is common.Major changes in the community can be seen with the addition of5m m Se VI to the soils,with only15and28%similarity for Msp I and Hha I,respectively,between anoxically incubated soils with and without Se VI.The natural microbial community is also affected by the combined addition of nitrate and Se VI, as,after four weeks,the community was only35–45%similar to Se VI-amended anoxic microcosms without nitrate and15–8% similar to nitrate-amended microcosms without Se VI.
These?ndings indicate that5m m Se VI could be toxic to much of the extant microbial community,and/or used as an electron acceptor by previously under-represented components of the community.However,the microbial community clearly does contain organisms that are able to survive in the conditions imposed,and to drive redox reactions resulting in the reduction of Se VI to Se0.The enrichment of these Se-resistant and/or reducing organisms is observed in the large change in microbial community in the presence of Se VI,contrasting with the lack of change in the unamended microcosms.
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Journal compilation?2013British Society of Soil Science,European Journal of Soil Science
8J.W.Fellowes et al
.
Figure 5Se EXAFS and Fourier transform for the anoxic +Se microcosm after 4weeks.Empirical data (solid lines)and ?tted model data (dashed lines)are
shown.
Figure 6(a)NMDS plot for the TRFLP data obtained from the County Meath microcosms using the 8F-FAM primer and Hha I restriction enzyme.(Cross)microcosm start,(open circle)microcosm after four weeks,(solid circle)microcosm after four weeks with Se VI ,(open square)microcosm after four weeks with nitrate,(solid square)microcosm after four weeks with nitrate and Se.(b)Dendrogram of TRFLP results using 8F-FAM primer and Hha I restriction enzyme.
Under the range of geochemical and microbial conditions tested in this study,the large concentration of Se naturally present in the soil at this ?eld site does not become bioavailable through release into the aqueous environment,but remains in the reduced Se form associated with the solid phase.Upon amendment with 5m m Se VI ,rapid microbially-driven reduction occurs and,under anoxic conditions,Se is completely removed from the aqueous phase within one week,with Se 0being the dominant reduced Se phase at the end of four weeks at 20?C.Given the larger rate of microbial activity and the abundance of electron donors,it is possible that the continued reduction of Se 0to Se II ?occurred within the microcosms,as previously reported for anoxic conditions (Herbel et al .,2003).The presence of aqueous,amorphous or crystalline selenide phases could not be con?rmed in these samples,suggesting that they formed a small component of the overall Se inventory and highlighting the dif?culties associated with analysis of mixed reduced Se systems.
The presence of alternative oxidants,such as oxygen or nitrate,has an inhibitory effect on the microbially-driven reduction of both Fe III and Se VI .The diminished rate of Fe III and Se VI reduction in nitrate-amended microcosms can be attributed to the large shift in microbial community.However,several contributory chemical and biological factors could also explain this reduction in activity.First,there will be direct competition between nitrate and selenate for recognition by nitrate reductases resulting from the greater af?nity of nitrate,and the preferential reduction of nitrate in systems where the concentration of nitrate is typically orders of magnitude greater than that of Se,as previously reported (Oremland et al .,1999;Sabaty et al .,2001).Second,in aqueous systems,the redox potential of the NO 3?/NO 2?couple (+0.42V)is similar to that of SeO 42?/SeO 32?(+0.44V)and so can directly compete with Se VI for reducing equivalents,inhibiting formation of an insol-uble Se 0phase (Steinberg et al .,1992;Masscheleyn &Patrick,1993;Zhang &Frankenberger,2007)Finally,the reoxidation of reduced Se phases by nitrate has been demonstrated and impli-cated in selenium toxicity in the western United States (Wright,1999).
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Journal compilation ?2013British Society of Soil Science,European Journal of Soil Science
Microbial soil selenium transformations9
Conclusions
This research has examined the geochemical and geo-microbiological characteristics of a naturally seleniferous soil located in County Meath,Ireland,?rst identi?ed by Fleming (1962).The?eld site remains highly seleniferous,with the 29–43-cm horizon containing156.2μg g?1Se as a reduced organic phase strongly associated with organic matter.The neg-ative correlation of selenium with depth as well as with various common rock-forming elements shows that the selenium does not originate from the underlying lithologies,but is probably a result of surface drainage into a post-glacial fen,as indicated by the strong correlation between Se and Sphagnum species biomarkers. The reduced organo-Se form is resistant to geochemical and microbiological degradation under a range of conditions for four weeks.Whilst the exact form of organo-Se has not been identi?ed,the formation and burial of a recalcitrant organo-Se phase within Sphagnum species plant matter is the probable concentration mechanism.
Active bacterial communities have been demonstrated within the seleniferous horizon,both by microcosm experiments and by lipid biomarker proxies,and the rapid removal of amended nitrate with little change in microbial community structure indicates that nitrate-reducing bacteria are prevalent.The strong correlation between bacterial biomarkers and Se concentrations is probably a function of the greater microbial activity in areas of abundant carbon sources,rather than an indication of a bacterial Se concentration mechanism.
Amendment of the soils with Se VI saw rapid,microbially-driven Se reduction producing the immobile,red elemental Se phase. The addition of nitrate hinders Se VI reduction,with resulting large shifts in the bacterial community structure,suggesting that the incumbent community could be largely intolerant to Se VI.These?ndings indicate that the addition of Se VI as a component of nitrogenous fertilizers may lead to a decrease in local Se immobilization,decreasing effectiveness as a fertilizer and increasing Se in surface runoff.The amendment of Se VI resulted in a large reduction in the diversity of the microbial population.Further research is required into the microbes that survive and play a role in the reduction of the toxic bioavailable Se.More extensive characterization of these microorganisms may lead to environmentally-friendly bio-remediation strategies as well as novel bio-mineralization techniques for the production of commercially relevant Se-bearing nanophases.
Supporting Information
The following supporting information is available in the online version of this article:
Table S1.Chemical composition of the seleniferous soil core pro?le showing key elements,determined by XRF.
Table S2.Pearson product-moment correlation coef?cients(r), regression equations with standard error of the coef?cients and coef?cients of determination(R2)for selected elements relative to selenium.Figure S1.(a)NMDS plot for the TRFLP data obtained from the Co.Meath microcosms using the1492R-HEX primer and Hha I restriction enzyme.(Cross)microcosm start,(open circle)microcosm four weeks,(solid circle)microcosm four weeks with Se VI,(open square)microcosm four weeks with nitrate, (solid square)microcosm four weeks with nitrate and Se.(b) Dendrogram of TRFLP results using1492R-HEX primer and Hha I restriction enzyme.
Figure S2.(a)NMDS plot for the TRFLP data obtained from the Co.Meath microcosms using the8F-FAM primer and Msp I restriction enzyme.(Cross)microcosm start,(open circle)microcosm four weeks,(solid circle)microcosm four weeks with Se VI,(open square)microcosm four weeks with nitrate, (solid square)microcosm four weeks with nitrate and Se.(b) Dendrogram of TRFLP results using8F-FAM primer and Msp I restriction enzyme.
Figure S3.(a)NMDS plot for the TRFLP data obtained from the Co.Meath microcosms using the1492R-HEX primer and Msp I restriction enzyme.(Cross)microcosm start,(open circle)microcosm four weeks,(solid circle)microcosm four weeks with Se VI,(open square)microcosm four weeks with nitrate, (solid square)microcosm four weeks with nitrate and Se.(b) Dendrogram of TRFLP results using1492R-HEX primer and Msp I restriction enzyme.
Acknowledgements
The authors especially wish to acknowledge the generous assistance of Garrett A.Fleming and Cian Condon(Teagasc, Ireland)in this work.The authors are very grateful for the support of P.Lythgoe,A.Bewsher(of the Manchester Analytical Geochemistry Unit,University of Manchester)and J.Waters (of the Williamson Research Centre,University of Manchester) for ICP,IC and XRD analyses,respectively.WAL gratefully acknowledges receipt of a PhD studentship funded by the Ministry of Manpower,Sultanate of Oman.XAS analyses were undertaken on ID26of the European Synchrotron Radiation Facility,6rue Jules Horowitz,BP220,F-38043Grenoble Cedex,France,with the beamline support of Dr K Kvashnina.Finally,the authors wish to acknowledge the?nancial support of NERC and RCUK. References
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Selenium安装以及简单的自动化测 试用例 中科软科技股份有限公司 2013年4月 V1.0.0
关于本文档 说明：类型－创建（C）、修改（U）、删除（D）、增加（A）；
目录 目录 (3) 1.Selenium介绍 (3) 2.相关组件 (3) 3.启动seleniumRC (4) 4.简单测试用例 (4) 4.1在火狐浏览器上下载并打开selenium IDE (5) 4.2录制测试用例 (6) 4.2.1 录制 (6) 4.2.2 检查 (6) 4.2.3 语言转换 (6) 4.2.4 准备Eclipse环境 (7) 4.2.5 运行 (9) 1.Selenium介绍 Selenium是一个用于Web应用程序测试的工具。Selenium测试直接运行在浏览器中，就像真正的用户在操作一样。支持的浏览器包括IE、Mozilla Firefox、Mozilla Suite等。 功能： ●测试直接在浏览器中运行，就像真实用户所做的一样，从终端用户的角度测试应用程序。 ●使浏览器兼容性测试自动化成为可能。 ●使用简单，可生成多种语言的用例脚本。 2.相关组件 ●Selenium IDE：一个Firefox插件，可以录制用户的基本操作，生成测试用例。随后可以 运行这些测试用例在浏览器里回放，可将测试用例转换为其他语言的自动化脚本。
●Selenium Remote Control (RC) ：支持多种平台(Windows，Linux，Solaris)和多种浏览器(IE， Firefox，Opera，Safari)，可以用多种语言(Java，Ruby，Python，Perl，PHP，C#)编写测试用例。 ●Selenium Grid ：允许Selenium-RC 针对规模庞大的测试案例集或者需要在不同环境中 运行的测试案例集进行扩展。 3.启动seleniumRC 官网下载：https://www.doczj.com/doc/df7592178.html,/download/。打开cmd，进入RC存放文件夹。在命令行输入：java –jar selenium-server.jar 。 启动成功。 注意在启动RC前，确认电脑上安装JDK版本高于1.5 4.简单测试用例 以OA系统登录为例：
Windows 下安装Selenium Webdriver ·安装ruby 下载地址https://www.doczj.com/doc/df7592178.html,/downloads/ 管理员运行：rubyinstaller-2.0.0-p247.exe，安装过程默认。勾选添加Ruby可执行到PATH 安装完成之后，进入命令行（Win+R）。后输入ruby –v gem –v 检测Rubygems是否是最新版本：gem update --system. Gem：类似于apple的app store 这样的东西。我们可以从里面安装所需的软件。例如Watir-Webdriver、selnium-webdriver等等。
·安装Selenium webdriver 控制台输入：gem install selenium-webdriver 查看是否安装成功：命令行输入：gem list selenium-webdriver 卸载方法：gem uninstall selenium-webdriver 查看文档： 1.命令行输入: gem server 2.浏览器输入：http://localhost:8808 3.找到“selenium-webdriver 2.3 4.0[rdoc]”点击rdoc进行相关文档 4. 搭建浏览器开发环境 下载IE driver server https://https://www.doczj.com/doc/df7592178.html,/p/selenium/downloads/list 下载Chrome driver https://https://www.doczj.com/doc/df7592178.html,/p/chromedriver/downloads/list 将driver文件放到系统的PATH中。（将下载下来的2个文件解压到Ruby的安装路径下的bin目录即可。例如：D:\Ruby200\bin） 注意：解压后的exe程序不可以重命名。 ·配置IE 配置IE的保护模式：工具->Internet选项->安全。4个选项卡要么全勾上，要么全部不勾选。
开源自动化测试工具selenium的使用 (玉米猫) 一Selenium概述： Selenium是现在使用最为广泛的一款开源自动化测试工具，也是非商业支持的稳定性易用性最好的一款自动化测试工具。和由HP提供强大商业支持的QTP相比，selenium不仅在软件投资上有比较大的优势，在针对web测试的稳定性上也有绝对的优势。以下介绍的内容会通过和QTP在各方面的比较中进行，并针对简单的测试样例，对基本的使用进行简单说明。 二Selenium的组成： 和QTP等其他工具类似，selenium也有几个组件组成，同时在使用的时候还需要一些开发的IDE平台进行支持。 对于初步的简单使用，需要先掌握seleniumIDE，RC的基本使用，以及对象识别方式Xpathe的基本知识。 1)seleniumIDE： selenium和QTP类似，同样需要先进行一定的脚本录制工作，而它默认支持的录制浏览器是firefox，IDE就充当了一个脚本记录的工作，它的表现形式为firefox的一款插件。 它可以记录准备过程中，用户在firefox上的制定网址下所做的一切操作，并转化为自己需要的一种开发语言，包括：java、perl、PHP、C#、Ruby等等。 2)RC： RC是selenium的特色组件，它通过从底层向不同的浏览器发出动作指令，达到用脚本控制web的效果，和QTP的activeX驱动的模式有着本质的不同，只要浏览器的动作指令原理不发生本质性的变化，就可以利用selenium达到自动化测试的效果，不会由于出现新的浏览器，还要等待HP重新开发相应的activeX控件。
3)其他： 由于selenium的非商业支持，所以很多类似于QTP中的组件都使用了firefox插件的办法得到了补充。 Firebug：帮助用户对页面上的对象进行识别，它可以准确捕捉到任何一个可见元素和不可见元素，同时支持由对象找代码和由代码找对象的使用方法，非常类似于QTP的spy 和控件高亮显示功能。 Xpather：帮助用户利用xpath标记对象的位置信息，根据xpath的实现方式，可以将页面上的每一个控件元素做唯一性标识，非常类似于QTP的对象库，区别在于Xpath只记录元素的位置样式属性，不会记录截图。 三Selenium的简单使用： 1)测试的准备工作： 这里所说的准备工作，只一个自动化测试的准备，预计基本的测试用例等内容已经准备完成。 假如被测系统为ADCPX： 首先：用firefox打开被测系统的首页，启动IDE插件。 需要注意的是，IDE的baseUrl一定是当前要测试的web首页，默认生成的第一个testcase 的名称可以通过属性进行更改。一个IDE中可以录制或生成多个testcase。
Windows下安装Selenium Webdriver ·安装ruby 下载地址https://www.doczj.com/doc/df7592178.html,/downloads/ 管理员运行：rubyinstaller-2.0.0-p247.exe，安装过程默认。勾选添加Ruby可执行到PATH 安装完成之后，进入命令行（Win+R）。后输入ruby–v gem–v 检测Rubygems是否是最新版本：gem update--system. Gem：类似于apple的app store这样的东西。我们可以从里面安装所需的软件。例如Watir-Webdriver、selnium-webdriver等等。
·安装Selenium webdriver 控制台输入：gem install selenium-webdriver 查看是否安装成功：命令行输入：gem list selenium-webdriver 卸载方法：gem uninstall selenium-webdriver 查看文档： 1.命令行输入:gem server 2.浏览器输入：http://localhost:8808 3. 4. 搭建浏览器开发环境 下载IE driver server https://https://www.doczj.com/doc/df7592178.html,/p/selenium/downloads/list 下载Chrome driver https://https://www.doczj.com/doc/df7592178.html,/p/chromedriver/downloads/list 将driver文件放到系统的PATH中。（将下载下来的2个文件解压到Ruby的安装路径下的bin目录即可。例如：D:\Ruby200\bin） 注意：解压后的exe程序不可以重命名。 ·配置IE 配置IE的保护模式：工具->Internet选项->安全。4个选项卡要么全勾上，要么全部不勾选。
selenium 自动化测试的框架 自动化测试的框架 软件自动化测试 style="font-family: 宋体 ;mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin;mso-fareast-font-family: 宋体 ;mso-fareast-theme-font: minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-the me-font:minor-latin"> 个阶段。 自动化测试的框架 软件自动化测试的框架和工具的发展大致将经历以下4个阶段。 https://www.doczj.com/doc/df7592178.html,/mengwuyoulin/article/details/44687317 自动化测试环境： [Selenium环境搭建安] 1、安装jdk. , 安装必须是在C盘里面 环境配置： C:\Program Files (x86)\Java\jdk1.6.0_10\bin C:\Program Files (x86)\Java\jdk1.6.0_10\lib 2、安装Firefox 3、下载selenium-ide 我下载的版本是selenium-ide-2.8.0.xpi selenium-ide安装：下载的selenium-ide-2.8.0.xpi拖到打 开的Firefox，（必须是后缀名为xpi的文件） 拖动到如下位置： 点击安装，根据提示重启Firefox浏览器 重启后，在菜单栏就可以看到Selenium IDE（没看到的到定制里面拖拽出来） 再在火狐浏览器上附加组件中搜索firebug，然后下载安装 4、Selenium-ide使用 Firefox窗口，菜单打开Selenium IDE 确认table无数据，Selenium IDE右上角红色按钮按下状态（默认就是按下的） 返回浏览器输入“测试IDE”，点击“搜索” 回到Selenium IDE，点击右上角红色按钮，停止记录 点击左上角“Play entire test suite”，可看见页面再重复刚才搜索的操作 注：type的value是搜索的关键值，修改value既可以把检索中输入的值修改 5、Selenium server的安装 下载selenium-server-standalone-2.45.0.jar 放到一个方便的文件夹下 6、启动Selenium server服务 Cmd 再进入elenium-server-standalone-2.45.0.jar 所在的目录下 java -jar selenium-server-standalone-2.45.0.jar 7、首先eclipse导入selenium-ide-2.8.0.xpi 解压后selenium-ide-2.8.0.jar 包 A、首先在建立项目下创建项目 Selenium自动化测试用例设计注意事项 UI元素映射 元素验证 等待加载 日志记录 结果收集 Selenium自动化测试用例设计注意事项（一） 自动化测试设计简介 我们在本章提供的信息，对自动化测试领域的新人和经验丰富的老手都是有用的。本篇中描述最常见的自动化测试类型，还描述了可以增强您的自动化测试套件可维护性和扩展性的“设计模式”。还没有使用这些技术的、有经验的自动化测试工程师会对这些技术更加感兴趣。 测试类型 您应该测试应用程序中的哪些部分这取决于您的项目的各种影响因素：用户的期望，时间期限，项目经理设置的优先事项等等。但是，一旦项目边界定义完成，作为测试工程师，你必须做出要测试什么的决定。 为了对Web应用的测试类型进行分类，我们在这里创建了一些术语。这些术语并不意味着标准，但是这些概念对web应用测试来说非常典型。 ● 测试静态内容 静态内容测试是最简单的测试，用于验证静态的、不变化的UI元素的存在性。例如： → 每个页面都有其预期的页面标题这可以用来验证链接指向一个预期的页面。 → 应用程序的主页包含一个应该在页面顶部的图片吗 → 网站的每一个页面是否都包含一个页脚区域来显示公司的联系方式，隐私政策，以及商标信息→ 每一页的标题文本都使用的selenium环境搭建
Selenium自动化测试用例设计注意事项
标签吗每个页面有正确的头部文本内吗 您可能需要或也可能不需要对页面内容进行自动化测试。如果您的网页内容是不易受到影响手工对内容进行测试就足够了。如果，例如您的应用文件的位置被移动，内容测试就非常有价值。 ● 测试链接 Web站点的一个常见错误为的失效的链接或链接指向无效页。链接测试涉及点各个链接和验证预期的页面是否存在。如果静态链接不经常更改，手动测试就足够。但是，如果你的网页设计师经常改变链接，或者文件不时被重定向，链接测试应该实现自动化。 ●功能测试 在您的应用程序中，需要测试应用的特定功能，需要一些类型的用户输入，并返回某种类型的结果。通常一个功能测试将涉及多个页面，一个基于表单的输入页面，其中包含若干输入字段、提交“和”取消“操作，以及一个或多个响应页面。用户输入可以通过文本输入域，复选框，下拉列表，或任何其他的浏览器所支持的输入。 功能测试通常是需要自动化测试的最复杂的测试类型，但也通常是最重要的。典型的测试是登录，注册网站账户，用户帐户操作，帐户设置变化，复杂的数据检索操作等等。功能测试通常对应着您的应用程序的描述应用特性或设计的使用场景。 ● 测试动态元素 通常一个网页元素都有一个唯一的标识符，用于唯一地定位该网页中的元素。通常情况下，唯一标识符用HTML标记的’id’属性或’name’属性来实现。这些标识符可以是一个静态的，即不变的、字符串
自动化测试环境： [Selenium环境搭建安] 1、安装jdk.,安装必须是在C盘里面 环境配置： 2、安装Firefox 3、 （必须是后缀名为xpi的文件） 拖动到如下位置： 点击安装，根据提示重启Firefox浏览器 重启后，在菜单栏就可以看到SeleniumIDE（没看到的到定制里面拖拽出来） 再在火狐浏览器上附加组件中搜索firebug，然后下载安装 4、Selenium-ide使用 Firefox窗口，菜单打开SeleniumIDE 确认table无数据，SeleniumIDE右上角红色按钮按下状态（默认就是按下的） 返回浏览器输入“测试IDE”，点击“搜索” 回到SeleniumIDE，点击右上角红色按钮，停止记录 点击左上角“Playentiretestsuite”，可看见页面再重复刚才搜索的操作注：type的value是搜索的关键值，修改value既可以把检索中输入的值修改 5、Seleniumserver的安装
放到一个方便的文件夹下 6、启动Seleniumserver服务 Cmd 再进入所在的目录下 7、首先eclipse导入解压后jar包 A、首先在建立项目下创建项目 B、项目下创建一个文件夹，保存我们的jar包。 在项目名上右击，依次点击【New】-->【Floder】，打开新建文件夹窗口c、 输入文件夹名称【lib】，点击【ok】。我们通常在lib文件夹中存放从外部引入的jar包 D、 找到我们要引入的jar包，鼠标选中jar包，然后按住鼠标左键不放，把jar 包拖到lib文件夹中。或先复制jar包，然后在lib文件夹上右击，选择复制。此时，打开选择框，我们选择默认的【copyfiles】，点击【OK】关闭。然后我们就可以在lib文件夹下看到我们复制成功的jar包。（注意，jar 包必须是.jar后缀名） E、此时，只是把jar包复制到项目中，还不能使用。我们再在项目名上右击，依次选择 【BuildPath】-->【ConfigureBuildPath...】。 F、在打开的窗口中，先选中【Libraries】页，再从右边的按钮中点击【addJARs...】
TAS Design Guide Author: peng gong Table of Contents 1 TAS模型介绍 (2) 1.1 Jenkins (2) 1.2 Python (3) 1.3 Selenium (3) 1.4 脚本代码管理：svn (3) 1.5 TAS运行环境：Linux+window (3) 2 TAS Frameworks (3) 2.1 测试管理：Jenkins (4) 2.2 脚本语言：Python (4) 2.2.1 Python2.7 (4) 2.2.2 Nose (4) 2.2.3 proboscis (5) 2.3 Web驱动：selenium (5) 3 TAS部署和要求 (5) 3.1 TAS环境要求 (5) 3.2 Jenkins和selenium安装 (5) 4 TAS运行和测试 (6) 4.1 测试运行 (6) 4.2 开发调试 (6) 4.3 开发调试工具 (6) 5 Code Frameworks (7) 5.1 Code结构 (7) 5.2 team模块举例 (7) 5.3 编码规范: (7) 5.4 A Simplest Example Script (8)
1.2 Python Python最大优点就是比其他语言更简单易学。同时Python自带的和大量开源的测试框架使得TAS系统架构更简单和便捷。TAS Frameworks使用了python自带的unittest拓展的开源nose和proboscis模块。 1.3 Selenium Selenium selenium是跨平台的web测试工具包。TAS选择selenium的原因在于： Selenium具有跨平台，跨浏览器的特点。 Selenium支持多种编程语言和测试框架。 Selenium工具包 TAS中使用了selenium RC驱动Web，开发工程师在开发script过程中可以使用selenium IDE和firebug等工具。 selenium运行 TAS中selenium有两种工作方式：服务器端和QA客户端。selenium运行在服务器端Jenkins和Selenium 交互，后者启动浏览器完成测试，返回结果给Jenkins。selenium运行在QA客户端的好处在于可以并行运行多个TAS测试任务。 1.4 脚本代码管理：svn TAS系统的脚本代码使用svn进行管理。测试中，Jenkins上配置svn的路径，Jenkins job开始构建时从svn中checkout最新版本进行测试。 1.5 TAS运行环境：Linux+window TAS系统的Jenkins安装在Server端的Linux/Ubuntu中，同时selenium也可以部署在Server上。测试工程师的PC上部署的selenium一般用于debug调试使用。 2 TAS Frameworks TAS框架主要由4部分组成，测试集成管理的Jenkins,Python脚本以及python 包,Selenium驱动模块和版本管理svn。详细模块拓扑图如下：
1、安装Firefox（最好默认路径安装，否则程序在打开Firefox时可能会出现问题）； 2、Selenium:selenium-java-2.39.0.zip, 解压selenium-java包； 3、新建一个Java project，然后把上面解压出来的文件拷到新建的project目录下，目录结构如下图: 4、添加build path，项目目录右键-->Build Path--> config build path-->Java Build Path-->Libraries-->Add JARs把libs文件夹下的jar包全部添加上，再添加selenium-java-2.39.0和selenium-java-2.39.0-srcs； 5、添加完之后目录结构如下图，多了Referenced Libraries,这里就是上面那一步添加进去的jar包：
6、关联webdriver的源码： 至此，环境工作准备就绪，下面来写一个简单的小例子。 7、在src下面新建测试类，如下图：
8、代码如下，主要是打开百度，然后在搜索框输入glen，点击搜索按钮，关闭浏览器。package com.selenium.Glen; import org.openqa.selenium.By; import org.openqa.selenium.WebDriver; import org.openqa.selenium.WebElement; import org.openqa.selenium.firefox.*; public class TestBuild { public static void main(String[] args) { //如果火狐浏览器没有默认安装在C盘，需要制定其路径 //System.setProperty("webdriver.firefox.bin", "D:/Program Files/Mozilla firefox/firefox.exe"); WebDriver driver = new FirefoxDriver(); driver.get("https://www.doczj.com/doc/df7592178.html,/"); driver.manage().window().maximize(); WebElement txtbox = driver.findElement(https://www.doczj.com/doc/df7592178.html,("wd")); txtbox.sendKeys("Glen"); WebElement btn = driver.findElement(By.id("su")); btn.click(); driver.close(); } } 然后直接右键-->Run As-->Java Application就可以看到效果了。
一、安装步骤 无网安装 前提：机子已安装Firefox24.0版本，若没有安装，请先安装Firefox浏览器24.0版本 1、python-2.7.6.msi安装程序包，双击运行安装即可，不用更改安装过程中的任何选项，既然你选择python，相信你 是熟悉python 的，我安装目录C:\Python27 2、setuptools-0.6c11.win32-py2.7的安装也非常简单，双击就可安装，不用更改安装过程中的任何选项，默认会找到python 的安装路径， 默认安装到C:\Python27\Lib\site-packages 目录下 3、打开命令提示符（开始---cmd 回车），输入命令python（如果提示python 不是内部或外部命令！别急，去配置一下环境变量吧） 修改 量名：PATH 变量值：;C:\Python27 我的电脑->属性->高级->环境变量->系统变量中的PATH 为: 变 5、安装selenium-2.40.0，先把selenium-2.40.0.tar.gz解压 到:C:\Python27\Lib\site-packages 目录下，打开命令提示符（开始---cmd 回车），使用cd命令进入C:\Python27\Lib\site-packages\ selenium-2.40.0目录下，输入python setup.py install回车，selenium安装完成 6、安装xlrd-0.9.2 ，先把xlrd-0.9.2.tar.gz解压到C:\xlrd-0.9.2 目录下，打开命令提示符（开始---cmd 回车）进入C:\xlrd-0.9.2目录下输入：python setup.py install，xlrd安装完成 9、打开火狐浏览器，把firebug-1.12.6-fx.xpi、webdriver.xpi、 selenium-ide-2.5.0.xpi分别拖入浏览器内，系统会提示安装，点击安装重启浏览器，右击火狐浏览器的右边工具栏处，选择定制工具栏，找到IDE，选中拖入右上角的工具栏处，IDE安装完成 9、开始菜单-所有程序-python27-右击pythonIDLE发送到桌面快捷方式，打开该窗口，用火狐打开任意界面，右击界面的任意一处，查看是否有使用firebug查看页面元素，有说明firebug安装成功 打开一python窗口，输入一下脚本保存XX.py，按F5运行，能打开iwebshop首页，并且关闭，python窗口不报错，说明配置环境安装完成 脚本：保存成.py文件 # coding=gbk from selenium import webdriver import time
Selenium自动化测试 一、目标和意义 a)掌握基本的自动化测试基础（过程，流程，定位方法） b)掌握初级脚本编写（参数化、打开文件，操作方法等） c)掌握单元测试套件的编写，自动化测试框架的设计和应用 二、课程安排 第一天 a)Web自动化测试的基础 b)Web自动化测试环境搭建 c)Python语言学习（上） 第二天 d)Python语言学习（下） e)Selenium-IDE工具的使用 f)Selenium初级脚本编写（定位；操作） 第三天 g)Selenium高级脚本编写（参数化， css/xpath定位） h)打开/写入文件、读取excel i)Pyunit单元测试框架介绍 第四天 j)测试套件的使用 k)测试报告的生成 l)测试框架的设计和应用 三、什么是自动化 由机器或工具代替手工执行软件测试，单击被测软件的界面，执行一系列操作并进行验证的过程 分类 功能自动化----QTP、Selenium 性能自动化----LR、Jmeter 白盒自动化----junit等 四、自动化测试的原理 a)手工测试 1、打开浏览器，访问iwebshop首页 2、点击登录按钮，进入登录页面 3、输入用户名，密码 4、点击登录按钮
5、系统提示登录成功，进入个人页面 b)自动化测试 1、调用webdriver函数打开浏览器，使用方法（get）访问目标网址 2、通过页面元素的属性定位登录按钮，使用方法（click）操作目标对象 3、通过页面元素的属性定位用户名/密码，使用方法（sendkeys）操作目标 对象 4、通过页面元素的属性定位登录按钮，使用方法（click）操作目标对象 5、定位实际结果并获取，比对实际结果与预期结果---断言 五、开展自动化测试的条件 1、手工测试基本通过 2、需求比较稳定，不易变更 3、自动化测试脚本可复用 4、项目周期足够长 5、手工测试无法完成时，需要投入大量的人力/物力 六、QTP与selenium工具的区别 七、Python—selenium自动化测试环境搭建 Os：xp、server、win7 1、安装Python--- python-2.7.6.msi，一路下一步，默认安装在C盘，配置path环境变量，追加Python安装目录C:\python27，验证：win+r打开运行，输入cmd进入dos环境，输入Python回车 查看是否进入Python环境。 2、安装setuptools-0.6c11.win32-py2.7.exe，一路下一步，默认安装。 3、安装selenium--- selenium-2.40.0.tar.gz， A、解压该压缩包，移动到C:\Python27\Lib\site-packages目录下，win+R 打开运行，输入cmd进入dos环境， B、使用cd命令进入C:\Python27\Lib\site-packages\selenium-2.40.0，输入dir查看setup.py文件 C、输入安装命令：Python setup.py install 回车