Development And Characterization Of Anaerobic Bacterial Enrichment Cultures That Extensively Dechlorinate Polychorinated Biphenyls

Polychlorinated biphenyls(PCBs)is one of the persistent organic pollutants.Bioremediation is regarded as a promising technology which can be applied in situ PCBs contaminated field,and the key to achieve successful remediation is anaerobic dechlorination of highly chlorinated congeners.Due to their slow growth rate and extremely low cell density,PCBs dechlorinators are difficult to be isolated.In order to have a better understanding of microbial dechlorination of PCBs.paddy soil was chosen as the source,Aroclor 1260,a commercial mixture of highly chlorinated PCBs,was used as the electron acceptor and lactate as the electron donor for the cultivation of PCBs dechlorinators.During the enrichment process,characteristics of PCBs dechlorination activity,variation in the abundance of dechlorinators as well as putative reductive dehalogenases(RDases),and dechlorinating microbial community were investigated.After six transfers,culture PSCJ-V which showed remarkable and stable dechlorination activity was further characterized.These six transfers could be divided into three stages:initial,transitory and stabilization stage.Detailed results are listed as below:(1)In the initial stage,it took relatively long lag phase for paddy soil culture to show its dechlorination capacity.While sediment was gradually diluted out from the culture during transitory stage,the rate of dechlorination was increased.Dehalococcoides mccartyi strains were identified as the main dechlorinator in PSCJ cultures.And from the functional gene screening results,five RDases(A1?A4?A5?Prd8?Prcd11)which shared high similarity with enzymes identified in D.mccartyi sp.CG1,CG4,CG5 and JNA were confirmed to be existed.It was observed that A1?Prd8 genes were gradually diluted out during transfers while A4?A5?Prd11 gene copies increased parallel with 16S rRNA gene copies.(2)After long period enrichment,sediment-free culture PSCJ-V showed rapidest and most extensive PCBs dechlorination capability,in which Aroclor 1260 could be dechlorinated within 40 days at an average rate of 5.6?mol L-1·day-1,mediating by Process N and Process LP.(3)Phylogenetical analysis showed that the PCBs dechlorinators in the culture PSCJ-V shared high similarity with Dehalococcoides mccartyi sp.CG4 and 195.Putative reductive dehalogenase(RDase)pcbPSCJ shared 97.7%amino acid sequence identity with the PCB-dechlorination-catalyzing PcbA5.(4)To have a comprehensive understanding of the microbial community in sediment-free PCB dechlorinating cultures,Illumina high throughput sequencing analysis was conducted.Results showed that the cultures were comprised mainly of the genus Dehalococcoides,Candidatus Cloacamonas,Smithella,Aminivibrio,Thermovirga,Proteiniphilum,Syntrophomonas,Sphaerochaeta,Youngiibacter,Desulfovibrio,Methanosarcina,Methanobacterium,Methanoculleus,Methanothrix,Methanomassiliicoccus.