Characterization of anaerobic microbial communities that adapt to 3-chlorobenzoate and 2-chlorophenol: An integrated approach of chemical measurements and molecular evaluations

The goal of this research was to improve our understanding of how microbial communities adapt to, and transform, initially recalcitrant compounds. Specifically, anaerobic sediment and digester sludge communities that adapt to 3-chlorobenzoate (3-CB) and 2-chlorophenol (2-CP) were characterized. DNA- and rRNA-based evaluations of community structure, metabolic perturbation experiments, and measurements of key biotransformation substrates and metabolites were integrated to link changes in community structure and function.; DNA-based evaluations of 3-CB-degrading sediment communities revealed that the structures of the adapted communities continued to change after degrading 3-CB for months. These evaluations also suggested that communities that share a common inoculum, but independently develop the ability to transform a chlorinated substrate, exhibit unique overall structures, yet share some common populations. Thus, the presence of the common populations may be necessary for a community to adapt to a chlorinated substrate.; Syntrophus-like populations were detected in 3-CB- and 2-CP-degrading communities using DNA-based techniques. rRNA-based evaluations quantitatively related the concentrations of Syntrophus-like populations and 3-CB or 2-CP transformation. The Syntrophus-like populations probably mediated fermentation of benzoate, a metabolite of anaerobic 3-CB and 2-CP biodegradation. rRNA-based evaluations and chemical measurements identified a correlation between Desulfovibrionaceae populations and 2-CP transformation in the sediment community; however, the nature of this relationship was not elucidated. Molecular perturbation experiments and DNA-based evaluations also pointed to a relationship between sulfate-reducing bacteria, in particular, Desulfomonile tiedjei-like populations, and reductive dehalogenation of 3-CB in sludge and sediment communities. Chemical measurements and rRNA-based techniques revealed that archaea in the sediment community benefited from the biodegradation of 3-CB and 2-CP, and metabolic perturbation experiments suggested that methanogens enhanced 3-CB transformation by consuming hydrogen.; The adaptation of the sludge and sediment communities to 3-CB, and of the sediment community to 2-CP, was reproducible. Therefore, it is unlikely that genetic changes contributed to adaptation in these systems. rRNA-based evaluations did not reveal any correlation between selective enrichment of targeted populations and adaptation to 3-CB or 2-CP. However, chemical measurements and metabolic perturbation experiments provided strong evidence that depletion of preferential organic substrates contributed to the adaptation of the digester sludge and sediment communities to 3-CB.