Bacteria Community Structure And BamA Gene Diversity In Anaerobic Degradation Of Toluene Under Denitrifying Condition In Coking Soil And Sludge

The coking contaminated soil accumulates a large amount of organic matter,which has the characteristics of high concentration,low biological availability,toxicity,recalcitrance and high remediation cost.The fewer the number of benzene ring of organic matter,the stronger of its solubility and migration.Besides,the deep soil environment is always lack of oxygen or in anaerobic condition.Therefore,this study chose toluene and benzoate as typical coking contaminants,and established nitrate-reducing enrichment cultures on toluene or benzoate in coking contaminated soil and sludge,respectively.The microbial properties of the cultures were studied by 16 s rRNA gene and ring opening bamA gene analysis,and the dominant bacteria were found out.The diversity of bamA gene was identified,and the application of bamA as a biomarker for ring cleavage in aromatics was discussed.The results will provide an important theoretical basis for the further research on anaerobic bioremediation of coking contaminated soil.The main conclusions are as follows:(1)In the enrichment cultures,the substrate loss and nitrate loss were synchronization.The actual molar ratios of toluene and benzoate consumption coupled with nitrate reduction were 1:8.7 和 1: 5.9,respectively,in coking soil enrichments,and the figures were 1:7.9 和 1.6.2,respectively,in coking sludge,which are all reasonably similar to the theoretical ratios.(2)On day 120 of coking soil enrichment cultures,the bacterial diversity of toluene and benzoate enrichments was less than that of background enrichments.The dominant phylum of toluene culture was Firmicutes,while the dominant phylum in benzoate culture was Proteobacteria.α-proteobacteria,γ-proteobacteria,and Bacilli were dominant classes in toluene enrichment,while the dominant class in benzoate enrichment was β-proteobacteria.The dominant genus of toluene culture were Exiguobacterium and Phyllobacterium,while Azoarcus is the dominant genus in benzoate culture.However,the microbial diversity in coking sludge was larger than that in coking soil.For the cultures enriched from coking sludge,the dominant phylum of both toluene and benzoate enrichments was Proteobacteria.The dominant classes in toluene and benzoate enrichments were α-proteobacteria and β-proteobacteria,respectively.The dominant genus in toluene and benzoate enrichments were Parvibaculum and Thauera,respectively.(3)Under denitrifying condition,in the toluene and benzoate cultures enriched from coking contaminated soil and coking sludge,most of bamA gene sequenced had the highest similarity and highest relative abundance with the bamA gene of Thauera chlorobenzoica.the diversity of bamA gene was relatively low,and the diversity of bamA gene in benzoate culture was larger than that in toluene culture.For bamA gene,Proteobacteria was the dominant phylum of both cultures.The dominant classes in toluene enrichment were β-proteobacteria and δ-proteobacteria,while β-proteobacteria was the dominant class in benzoate enrichment.Thauera chlorobenzoica was the dominant genus of toluene culture,while Azoarcus was the dominant genus of benzoate culture.