Influence of non-dechlorinating microbes on trichloroethene reduction based on vitamin B12 synthesis in anaerobic cultures

In this study, the YH consortium, an ethene-producing culture, was used to evaluate the effect of vitamin B12 (VB12) on trichloroethene (TCE) dechlorination by transferring the original TCE-reducing culture with or without adding exogenous VB12. Ultra-high performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) was applied to detect the concentrations of VB12 and its lower ligand 5,6-dimethylbenzimidazole (DMB) in the cultures. After three successive VB12 starvation cycles, the dechlorination of TCE stopped mostly at cis-dichloroethene (cDCE), and no ethene was found; methane production increased significantly, and no VB12 was detected. Results suggest that the co-cultured microbes may not be able to provide enough VB12 as a cofactor for the growth of Dehalococcoides in the YH culture, possibly due to the competition for corrinoids between Dehalococcoides and methanogens. The relative abundances of 16 S rRNA gene of Dehalococcoides and reductive dehalogenase genes tceA or vcrA were lower in the cultures without VB12 compared with the cultures with VB12. VB12 limitation changed the microbial community structures of the consortia. In the absence of VB12, the microbial community shifted from dominance of Chloroflexi to Proteobacteria after three consecutive VB12 starvation cycles, and the dechlorinating genus Dehalococcoides declined from 42.9% to 13.5%. In addition, Geobacter, Clostridium, and Desulfovibrio were also present in the cultures without VB12. Furthermore, the abundance of archaea increased under VB12 limited conditions. Methanobacterium and Methanosarcina were the predominant archaea in the culture without VB12.