ht t p : / / w w w . b j m i c r o b i o l . c o m . b r /
Environmental
Microbiology
Decolorization
of
azo
dyes
(Direct
Blue
151
and
Direct
Red
31)
by
moderately
alkaliphilic
bacterial
consortium
Sylvine
Lalnunhlimi,
Veenagayathri
Krishnaswamy
∗DepartmentofBiotechnology,StellaMarisCollege,Chennai87,Tamilnadu,India
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t
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c
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e
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o
Articlehistory:Received12July2014 Accepted2May2015 AssociateEditor:RaquelSilva Peixoto
Keywords:
Alkaliphilicbacterialconsortium Azodye DirectBlue151 DirectRed31 Decolorization Salinity
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b
s
t
r
a
c
t
Removalofsyntheticdyesisoneofthemainchallengesbeforereleasingthewastes dis-chargedbytextileindustries.Biodegradationofazodyesbyalkaliphilicbacterialconsortium isoneoftheenvironmental-friendlymethodsusedfortheremovalofdyesfromtextile effluents.Hence,thisstudypresentsisolationofabacterialconsortiumfromsoilsamples ofsalineenvironmentanditsuseforthedecolorizationofazodyes,DirectBlue151(DB 151)andDirectRed31(DR31).Thedecolorizationofazodyeswasstudiedatvarious con-centrations(100–300mg/L).Thebacterialconsortium,whensubjectedtoanapplicationof 200mg/Lofthedyes,decolorizedDB151andDR31by97.57%and95.25%respectively,within 5days.ThegrowthofthebacterialconsortiumwasoptimizedwithpH,temperature,and carbonandnitrogensources;anddecolorizationofazodyeswasanalyzed.Inthisstudy, thedecolorizationefficiencyofmixeddyeswasimprovedwithyeastextractandsucrose, whichwereusedasnitrogenandcarbonsources,respectively.Suchanalkaliphilicbacterial consortiumcanbeusedintheremovalofazodyesfromcontaminatedsalineenvironment. ©2015SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.Thisis anopenaccessarticleundertheCCBY-NC-NDlicense
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
Anumberofcoloredeffluentsthatcontaindyesarereleased fromtextile,food,leather,dyestuff,anddyeingindustries.The textileindustryisoneofthelargestproducersofeffluents con-taminatedwithdyes.1Theresidualdyesreleasedfromthese
effluentsintroducedifferentorganicpollutantsinthenatural waterresourcesandland.2
∗ Correspondingauthor.
E-mail:[email protected](K.Veenagayathri).
Approximately 80,000tonsofdyestuff and pigmentsare producedinIndia.1 Ithasbeenestimatedthat10,000
differ-enttextiledyesarecommerciallyavailableworldwideandthe annualproductionisestimatedtobe7×105metrictons;30%
ofthesedyesareusedinexcessthatis1000tonsperannum.3–5
Duringthedyingprocess,about2%ofthesedyesfailtobind tothesubstrateandaredischargedinaqueouseffluents.6Azo
dyesarethemostwidelyuseddyesintheindustrialsector.7
Theycontainoneormoreazogroups( N N)thatcanresist thebreakdownand accumulateintheenvironmentathigh levelswithhighdegreeofpersistence.8,9
The wastewater from textile when directly released in the surface water without treatment can cause a rapid
http://dx.doi.org/10.1016/j.bjm.2015.11.013
1517-8382/©2015SociedadeBrasileiradeMicrobiologia.PublishedbyElsevierEditoraLtda.ThisisanopenaccessarticleundertheCC BY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).
depletionofdissolvedoxygenandleadtoagreat environmen-taldamage.10 Whendyesareavailableinthewatersystem,
thesunlightpenetrationintodeeperlayersisgreatlyreduced whichdisturbsphotosyntheticactivityresultingin deteriora-tionofwaterquality,loweringthegassolubility,andfinally causesacutetoxiceffectsonaquaticfloraandfauna.Mostof thedyesthatare releasedfromwastewater,includingtheir breakdownproducts,aretoxic,carcinogenic,ormutagenicto humansandotherlifeforms.11,12
Various physicochemical methods, such as adsorption on activated carbon, electrocoagulation, flocculation, froth flotation,ionexchange,membranefiltration,ozonation,and reverse osmosis,are used forthedecolorization ofdyesin wastewater.Thesemethodsare inefficient,expensive,have lessapplicability,andproducewastesintheformofsludge, whichagainneedstobedisposedoff.13
However,themicrobialdecolorizationanddegradationof azodyeshasgainedconsiderableinterestofresearchersas itisinexpensive,eco-friendly,andproduceslessamountof sludge.14,15 Ithas been reported that many organisms are
capableofreducingdyes,suchaspurelyanaerobic(e.g., Bac-teroidesspp.,Eubacteriumspp.,Clostridiumspp.),facultatively anaerobic(e.g.,Proteusvulgaris,Streptococcusfaecalis),aerobic (e.g.,Bacillusspp.,Sphingomonasspp.),severalyeasts,andeven tissuesfromhigherorganisms.16–22
Effluentsreleasedfromtextilesindustriesaretoxic,which containahighdegreeofcolor(fromresiduesofreactivedyes andchemicals)alongwithacidicandalkalinecontaminants andhighconcentrationsoforganicmaterials.23Extremophiles
(alkaliphilesandhalophiles)aremetabolicallydiverseandcan usuallytolerateagreateramountoftoxicmetalsandalkaline conditionsintheirenvironment.24Thisstudyfocusesonthe
decolorizationofazodyesbyamoderatelyalkaliphilic bacte-rialconsortiumisolatedfromsalinesoilsamples.Theisolated bacterialconsortiumwasusedinthe decolorizationofazo dyesDirectBlue 151(DB 151)and DirectRed 31(DR31) at differentconcentrations.Thegrowthparametersforthe con-sortiumwereoptimized.Thebacterialstrainspresentinthe consortiumwereidentifiedby16SrDNAsequencing.
Materials
and
methods
Dyesandchemicals
Thetextiledyes(azodyecompounds),namelyDR31andDB 151,werepurchasedfromthetextileindustry.Nutrientagar mediaandallotherchemicalsusedinmineralsaltmedium (MSM)preparation were ofanalytical gradeand purchased fromMerck,India.
Bacterialconsortiumandcultureconditions
Thebacterialconsortiumwasisolated fromsoilsamplesof salineenvironmentfromthreedifferentregionsofChennai, namely Nagercoil,Tuticorin, and Pallavaram. The bacterial consortiumwas enriched in MSM amended with 100mg/L of DB 151 and DR 31. The composition of the MSM (pH 9) used forenrichment and decolorization was as follows: Na2HPO4: 12.8g/L;KH2PO4: 3g/L; NH4Cl: 1g/L;NaCl:0.5g/L;
0.05MMgSO4:10mL/L; 0.01MCaCl2:10mL/L;and 20%
glu-cose:30mL/L.9Themediumwasautoclaved,cooled,andthen
amendedwith100mg/LoffiltersterilizedDB151andDR31in a250mLErlenmeyerflask.Anamountof10gofsoilsample wasasepticallyinoculatedintothemedium.Individual bacte-rialisolateswereobtainedfromtheenrichedculturebyplating onnutrientagarmediumcontaining100mg/LofDB151and DR31.Theselectedisolateswerethenpurifiedbystreaking onnutrientagaraddedwith100mg/Lofthedyes.Thesingle colonypurecultureswerestoredin15%glycerolat20◦C.
Analyticaltechniques
All decolorization experiments were carried out multiple times. MSM addedwithazo dyeswasused asacontrolto determine abiotic color loss duringthe experiment. A vol-umeof1mLofpreculturedbacterialconsortiumwasaddedto 50mLofMSMaddedwithdifferentconcentrations(100,150, 200, 250,and300mg/L)ofDB151andDR31.The biodecol-orizationofDB151and DR31 bybacterialconsortiumwas observedfor5days25.Inordertomonitorthedecolorization
process,thesampleswerewithdrawnperiodically,centrifuged at10,000rpmfor15min, andfilteredthrough syringefilter (PVDF,Millipore,Inc.);anddecolorizationwasmeasuredusing UV/Visspectra(Hitachi)atthecorrespondingmaxofthedye
andwascomparedwiththeuninoculatedcontrol.Thetotal proteincontentwasalsoestimatedatevery 24h.Thecolor removalefficiencyofthebacterialconsortiumwasdetermined asfollows26:
Decolorization (%)
= Initialabsorbance−Observedabsorbance Initialabsorbance
EffectofpHandtemperatureonthedecolorizationof mixeddyes
InordertostudytheeffectofpHandtemperature,the steril-izedMSMwasamendedwith200mg/LofeachoftheDB151 andDR31dyes.ThemediumwasmaintainedatdifferentpH: 8,8.5,9,9.5,and10.Avolumeof1mLofovernightculturewas inoculatedintheflasksandincubatedinashakerat36◦C.The effect oftemperaturewas studiedbyinoculating overnight cultureandincubatinginashakerat28◦C,36◦C,and45◦C. ThemediumwasmaintainedatpH9.5.Themeasurementof decolorizationofthetotaldyeconcentrationwasperformed atanintervalof24hfor5days.
Effectofcarbonandnitrogensourcesonthedecolorization ofmixeddyes
Theeffectofcarbonsourceswasstudiedusingvarious com-pounds,suchasfructose,lactose,sucrose,andmannitol,at aconcentrationof1%andtheywereaddedindividuallyasa supplementtoMSMforthedecolorizationofmixeddyes.A volumeof1mLoftheovernightculturewasinoculatedinthe flasksandincubatedinashakerat36◦C.Nitrogensources, suchasyeastextract,KNO3,NaNO3,andNH4NO3wereadded
Bacillus flexus strain NBN2 16S ribosomal RNA gene partial sequence. (SY1)
Bacillus cereus strain AGP-03 16S ribosomal RNA gene partial sequence. (SY2)
Bacillus cytotoxicus NVH 391-98 complete genome. (SY3)
Bacillus sp. L10 16S ribosomal RNA gene partial sequence. (SY4)
1 70
Fig.1–Phylogenetictreeoftheisolatedbacterialstrains,identifiedthrough16Sr-DNAsequencingshowingthe evolutionaryrelationship.
toMSM at aconcentration of 0.5%;and 1mL ofovernight culturewasincubated at36◦C.Inordertostudy theeffect ofefficientcarbonand nitrogensources,the optimum car-bonandnitrogensources,i.e.,sucroseandyeastextract,were addedtoMSMataconcentrationof1%and0.5%,respectively, andthedecolorizationofthedyeswasmeasured.
Identificationofazo-dyedegradingbacterialstrains
Theindividualbacterialstrainswereseparatedfromthe con-sortium,andwereusedforthedegradationoftheazodyes. The bacterial strains present in the consortium were ini-tially examined using conventional biochemical tests. The molecularidentificationofthebacterialstrainswasperformed by 16S rDNA sequencing. The bacterial strains present in theconsortiumwereisolatedandgrownseparately.Initially, Gramstainingand motilitytests wereperformed andthen thebiochemicalcharacterizationwas carriedout for differ-entparameters(catalase,oxidase,indoleproduction,citrate utilization, methyl red, Voges Proskauer, triple sugar iron agar,andurease)using24holdcultureofindividual bacte-rialstrains.After24hofincubationat37◦C,thecolorchange observedwas accountedfora positive/negativeresult. The genuslevelidentificationoftheunknownbacterialstrainswas carriedoutusingBergey’sManualofSystematicBacteriology (2005)toascertaintheexistenceofvariablebiochemicaltest resultsforeachstrain.
16SrDNApartialgenesequencing
Chromosomal DNA was isolated from pure strains of the consortium by the standard phenol/chloroform extraction method(Sambrook).The1.5kbpartialsequenceof16SrDNA gene was amplified by the chromosomal DNA using poly-merasechainreaction(PCR)withuniversalEubacteria-specific primers 16F27 (5-CCA GAG TTT GAT CMT GGC TCA G-3) and16R1525XP(5-TTCTGCAGTCTAGAAGGAGGTGWTCCA GCC-3).27TheusedPCRconditionswere:initialdenaturation
at94◦C for2min, followedby35 cycles ofdenaturationat 95◦C for 1min, annealing at 55◦C for 1min, extension at 72◦Cfor1min,andafinalextensionat72◦Cfor10min;and finallysequencing wasperformedonanABI310-automated DNAsequencerusingBigDyeterminatorkit(Applied Biosys-tems 3730xl DNA Analyzer). The amplified16S rDNA gene (PCRproducts) from these isolateswas directly sequenced afterpurificationbyprecipitationwithpolyethyleneglycoland
NaCl.Theprimersusedtoobtainthecompletesequenceof 16SrDNAgeneoftheisolateswerethesameasusedforthe PCRamplification(16F27Nand16R1525XP).
SequencedataanalysiswasperformedusingChromasPro sequenceanalysissoftware.Thephylogenetictreewas con-structedbyMEGA5.28Theevolutionaryhistorywasinferred
usingtheneighbor-joiningmethod.Theoptimaltreewiththe sumofabranchlengthof0.18268090isshown.Thetreewas drawntoscalewithbranchlengths(nexttothebranches)in thesameunitsasthoseoftheevolutionarydistancesusedto inferthephylogenetictree.Theevolutionarydistanceswere computed using the Kimura two-parameter method29 and
were in the units ofthe number of basesubstitutions per site.Theanalysisinvolvedthreenucleotidesequences.The codonpositionsincludedwerefirst,second,thirdnoncoding
0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0
Decolorization of direct blue 151 (%)
Time(d) 100 ppm 150 ppm 200 ppm 250 ppm 300 ppm Abiotic control 0 1 2 3 4 5 6 7 8 9 10 5 4 3 2 1 0 Total protein (mg/ml) Time(d) 100 ppm 150 ppm 200 ppm 250 ppm 300 ppm Abiotic control
Fig.2–DecolorizationofDB151atdifferentconcentrations bythebacterialconsortium.
0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0
Decolorization of direct red 31 (%)
Time(d) 100 ppm 150 ppm 200 ppm 250 ppm 300 ppm Abiotic control 0 1 2 3 4 5 6 7 8 9 10 5 4 3 2 1 0 Total protein (mg/ml) Time(d) 100 ppm 150 ppm 200 ppm 250 ppm 300 ppm
Fig.3–DecolorizationofDR31atdifferentconcentrations bythebacterialconsortium.
sequences.All positions containinggaps and missing data wereeliminated.Therewereatotalof1065positionsinthe finaldataset.Theevolutionaryanalyseswereconductedby MEGA5.30
Results
and
discussion
Azo dyes are widely used in many industries. These azo dyeshavebeen showntobereductively cleavedbyawide rangeofmicroorganisms.Bothaerobicandanaerobic bacte-riafromdifferentenvironmentspossesstheabilitytoreduce azodyesintogenotoxiccompounds.Thisstudyaimsto iso-late alkaliphilic bacterial consortium that can be used for the removal ofmixed dyes as textile wastes tend to have highpH.
Isolationandscreeningofazo-dyedegradingbacterial consortium
Theinitialenrichmentofthebacterialconsortiumforthe azo-dyedegradationindicatedfourbacterialstrainsdesignatedas SY1,SY2,SY3,andSY4tobeefficient.Allofthefourbacterial isolateswerefurthergrownonMSM-containingagarwithout additionofany carbonand nitrogensources.Theyshowed theabilitytogrowontheMSMagarafter48hofincubation at37◦C.Thescreeningexperimentsforcolorremovalwere carriedoutunderalkalinepHandaerobicconditions.
0 1 2 3 4 5 6 7 8 9 10 5 4 3 2 1 0 Total protein (mg/ml) Time(d) pH 8 pH 8.5 pH 9 pH 9.5 0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0
Decolorization of mixed dyes (%)
Time (d)
pH 8 pH 8.5 pH 9 pH 9.5
Fig.4–Decolorizationofthemixeddyes(200ppm)bythe bacterialconsortiumatdifferentpH.
Sequenceanalysesofgeneencodingfor16SrDNAfrom thebacterialisolates
The phylogenetic tree(Fig. 1) constructedbyMEGA530
dis-playeda relationbetweenall the isolatedbacterial strains. TheisolateswereidentifiedasBacillusflexusstrainNBN2(SY1),
BacilluscereusstrainAGP-03(SY2),BacilluscytotoxicusNVH 391-98(SY3),andBacillussp.L10(SY4).
Azo-dyedecolorizationatvariousconcentrations
The bacterial consortium that contains the four strains enrichedinthesoilsamplesofsalineenvironmentwasused foranalyzingazo-dyedecolorization.Theabilityofthe bac-terialconsortiumtodecolorize thedyesDB151and DR31, atvariousconcentrations (100,150,200, 250,and 300mg/L) was investigated.Therate ofdecolorizationincreasedwith increase in initialdyeconcentration from 100 to200mg/L, whereasdecolorizationdecreasedat250mg/Lwhichfurther continuedtodecreaseat300mg/L.Thetotalproteincontent anddecolorizationatvariousconcentrationsofthedyesDB 151andDR31areshowninFigs.2and3.
Earlier studies ondecolorization atvarious dye concen-trationshavebeenperformedundernon-alkalineconditions. These studies have shown the negative effect of increas-ingdyeconcentrationfromoptimallevelondyedecolorizing efficiency.31–34Thisstudywasconductedunderalkaline
con-ditions.ThedecolorizationofDB151andDR31increasedfrom 100to150mg/L,i.e.,96%and97%onthe5thday.Theoptimum concentrationforefficientdyedegradationwasfoundtobe 200mg/LforDB151andDR31,where97.57%and95.25%ofthe
0 1 2 3 4 5 6 7 8 9 10 5 4 3 2 1 0 Total protein (mg/ml) Time(d) 28 °C 36 °C 45 °C Abiotic control 0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0
Decolorization of mixed dyes (%)
Time (d) 28 °C
36 °C 45 °C Abiotic control
Fig.5–Decolorizationofthemixeddyes(200ppm)bythe bacterialconsortiumatdifferenttemperatures.
dyesweredegraded,respectively.Thetotalproteincontentof thebacterialconsortiumincreased,at200mg/LofDB151and DR31,from6.62to9.4mg/mLand7.41 to9.41mg/mLfrom 1stto3rdday,respectively.WhentheconcentrationofDB151 wasincreasedto250mg/L,thedecolorizationofDB151and DR31wasreducedto93.99%and91.56%,respectively. Decol-orizationat300mg/LofDB151andDR31showed91.89%and 90.08%reduction,respectively.
EffectofpH
ThepHtoleranceofdecolorizingbacteriaisquiteimportant becausereactiveazodyesareboundtocottonfibersby addi-tion orsubstitution mechanisms underalkalineconditions andhightemperatures.35TheeffectofpHwasstudiedat
dif-ferentpHs(8,8.5,9,9.5,and10).AllthepHsallowedgrowthof thebacterialconsortium.Themaximumdecolorizationwas observedatpH9.5,whichwas87%bytheendofthe5thday. ThiswasfollowedbypH10,9,8.5,and8,whichshowed85%, 83.2%,80.86%,and78%ofdecolorization,respectively,bythe endofthe5thday(Fig.4).
Effectoftemperature
Theeffectoftemperaturewasanalyzedat28◦C,36◦C,and 45◦C.Thetemperature36◦Cenhancedthegrowthofthe bac-terial consortiumand showed maximum decolorization of mixeddyesthatwas87.49%bytheendofthe5thday.Thiswas
0 1 2 3 4 5 6 7 8 9 10 5 4 3 2 1 0 Total protein (mg/ml) Time(d) Fructose Lactose Sucrose Mannitol Abiotic control 0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0
Decolorization of mixed dyes (%)
Time (d) Fructose Lactose Sucrose Mannitol Abiotic control
Fig.6–Decolorizationofthemixeddyes(200ppm)bythe bacterialconsortiumwithdifferentcarbonsources.
followedby45◦Cwhichshoweddecolorizationupto85.39%. Thetemperature28◦Cshowedtheleastdecolorizationofthe mixeddyesthatwas50%onthe5thday(Fig.5).Theseresults concordwithanearlierstudyontheeffectofvarious temper-atures(25–40◦C)onthedecolorizationofFastRedbyBacillus subtilis,whereinthemaximumdecolorizationwasobserved at30–35◦C.36
Effectofcarbonsources
To examine the influence ofcarbon sources on the decol-orizationofmixed dyes(200mg/L),carbon sourcessuchas lactose,sucrose,mannitol,andfructose,weresupplemented inthemedia.Itwasfoundthatsucrosecouldenhance the growthofthebacterialconsortiummoreeffectivelythanother carbon sources (Fig. 6). The decolorization of mixed dyes reachedamaximumof90.62%withsucroseasacarbonsource followed by fructose, lactose, and mannitol which showed 89.08%,88.11%,and87.69%ofdecolorization,respectively.A similarobservationwasmadebyPonrajetal.37whoreported
therangeofactivityonthedecolorizationofOrange3Rwith 1%sucroseasa carbonsourcebyBacillus sp.,Klebsiellasp.,
Salmonellasp.,and Pseudomonassp.,showingdecolorization of87.80%,72.36%,86.18%,and80.49%,respectively,withthe bacteriumBacillussp.asthemosteffectivedecolorizerwith sucroseasacarbonsource.
0 1 2 3 4 5 6 7 8 9 10 5 4 3 2 1 0 T o ta l prot ei n ( m g/ m l) Time (d) Yeast extract KNO3 NaNO3 NH4NO3 Abiotic control 0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0 De co lo ri z a ti on of m ixe d d y e s (%) Time (d) Yeast extract KNO3 NaNO3 NH4NO3 Abiotic control
Fig.7–Decolorizationofthemixeddyes(200ppm)bythe bacterialconsortiumwithdifferentnitrogensources.
Effectofnitrogensources
Organicnitrogensourcesareconsideredessentialmedia sup-plementsfortheregenerationofNADHthatactsasanelectron donor for the reduction of azo dyesby microorganisms.38
Nitrogensourcesusedinthisstudywere0.5%eitherofyeast extract, potassiumnitrate (KNO3), sodium nitrate (NaNO3),
and ammonium nitrate (NH4NO3), supplemented in MSM
alongwithDB151andDR31at200mg/L(Fig.7).Yeastextract showedamaximumdecolorizationof92.73%bytheendofthe 5thday,whichwasfollowedbyNaNO3,NH4NO3,andKNO3.A
reportontheeffectofvariousnitrogensources,suchasyeast extract,meatextract,peptone,andurea(0.5%)concurswith ourstudy,wherein theused bacterialstrainsutilized yeast extractmosteffectively.7
Effectofmixedcarbonandnitrogensourcesonthe decolorizationofmixeddyes
Toincreasethedyedegradationefficiency,sucroseandyeast extract(1%and0.5%)wereaddedtothemedia.Theadditionof acombinationofyeastextractandsucrosefurtherenhanced thedecolorizationofmixeddyesby94%attheendofthe5th day(Fig.8).
Decolorizationofmixeddyesbyindividualisolates
Individualbacterialstrainswereanalyzedforthe decoloriza-tionofmixeddyesDB151andDR31at200mg/L(Fig.9).B. cereusshowedmaximumdecolorizationof93.37%formixed
0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0
Decolorization of mixed dyes (%)
Time(d)
Sucrose + yeast extract Abiotic control 0 2 4 6 8 10 12 5 4 3 2 1 0 Total protein (mg/ml) Time (d) Sucrose + yeast extract Abiotic control
Fig.8–Decolorizationofthemixeddyes(200ppm)bythe bacterialconsortiumwithmixedcarbonandnitrogen sources. 0 1 2 3 4 5 6 7 8 9 10 5 4 3 2 1 0 Total protein (mg/ml) Time (d) SY1 SY2 SY3 SY4 Abiotic control 0 10 20 30 40 50 60 70 80 90 100 5 4 3 2 1 0
Decolorization of direct blue 151 (%)
Time (d) SY1 SY2 SY3 SY4 Abiotic control
Fig.9–DegradationofDirectBlue151bythebacterial isolatesandtotalproteincontentofthebacterial consortium.
dyesunderoptimumconditions.ThiswasfollowedbyB. cyto-toxicus,Bacillussp.L10,andB.flexusshowing92.77%,86.86%, and 85% decolorization,respectively. Astudy conductedby Ponrajetal.37showedthatBacillussp.hashighdecolorizing
capacityfor Orange 3R.They isolated Bacillus sp., Klebsiella
sp.,Salmonellasp.,andPseudomonassp.fromtextileeffluent andanalyzedthedecolorizationofOrange3Runderoptimum conditionsandreportedthatBacillussp.andPseudomonassp. showedasimilarlevelofdecolorization(89%)followedby80% and76%bySalmonellasp.andKlebsiellasp.,respectively.
Conclusion
Thisstudyreportsthatanenrichedbacterialconsortiumcan efficiently decolorize DB151 and DR 31 up to 97.57% and 95.25%,respectivelyin5days.Thebacterialconsortium exhib-itedmaximumdecolorizationabilityofmixeddyesatpH9.5. ThephysicalparameterssuchaspH,temperature,andcarbon andnitrogensourcesplayanimportantroleinenhancingof thedecolorizationefficiency.Theindividualisolateswerealso abletodegradethemixeddyes.AstrainofB.cereusshowed maximumdecolorization abilityofup to93.37% in5days. However,futureworkontheidentificationofgenespresent inthebacterialstrainscanbehelpfulinenhancingthe decol-orizationofazodyes.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
Authors’
contributions
KVGconceivedthestudy,participatedinitsdesignanddrafted themanuscript;SYimplementedtheexperimentalworkand helped in drafting the manuscript. All authors read and approvedthefinalmanuscript.
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