Enrichment, isolation, and characterization of reductively dechlorinating microorganisms from coastal marine sediments

Most of the halogenated natural chemicals are produced in marine habitats but the existence of dechlorinating microbes in this environment has not been explored. Such organisms could be important in pollutant cleanup in harbors. Seven coastal marine sediments were tested in sediment microcosms for reductive dechlorination activity on four chloroaromatic compounds, 2-chlorophenol (2-CP), 2,4,6-trichlorophenol (2,4,6-TCP), 3-chlorobenzoate (3-CB), and 3-chlorotoluene (3-CT). 2-CP and 3-CB dechlorination activities were sustained in sediment microcosms and enrichment cultures in synthetic seawater medium, whereas 2,4,6-TCP dechlorinating activity was lost. Microbial characterization of the 3-CB dechlorinating cultures by ARDRA (amplified ribosomal DNA restriction analysis) and 16S rRNA sequence analysis showed that the patterns of the dominant clones shifted when the cultures were more highly enriched.;Two anaerobic dechlorinating microorganisms, strains SF3 from San Francisco Bay sediment and DCB-M from Gulf Breeze, FL sediment, were isolated and characterized. Strain SF3 is a gram-negative, motile, short curved rod that grows by coupling reductive dechlorination of 2-CP to acetate oxidation. Strain SF3 also used fumarate, sulfate, sulfite, thiosulfate, and nitrate as electron acceptors for growth and grew at sodium chloride concentrations ranging from freshwater to seawater. Growth by halorespiration was confirmed by the growth yield of 1 g of protein per mole of 2-CP dechlorinated. Morphology, physiology, and 16S rRNA sequence analysis indicated that this organism belongs to the Desulfovibrio group of the sulfate-reducing bacteria and represents a novel genus. Strain DCB-M is a gram-negative, nonmotile, long rod with a collar girdling the cell, and is capable of growth by reductive dechlorination of 3-CB to benzoate. Strain DCB-M grew in seawater medium but was not capable of growth in the freshwater concentration of sodium chloride. The growth yield was 1.7 g of protein per mole of 3-CB dechlorinated. Strain DCB-M's 16S rRNA sequence places it in the delta proteobacteria and close to Desulfomonile tiedjei strain DCB-1. The morphology, physiology, and 16S rRNA sequence suggest that strain DCB-M is a marine relative of Desulfomonile tiedjei strain DCB-1.