Phylogenetic characterization of a polychlorinated-dioxin- dechlorinating microbial community by use of microcosm studies.
Microcosms capable of reductive dechlorination of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) were constructed in glass bottles by seeding them with a polluted river sediment and incubating them anaerobically with an organic medium. All of the PCDD/F congeners detected were equally reduced without the accumulation of significant amounts of less-chlorinated congeners as the intermediate or end products. Alternatively, large amounts of catechol and salicylic acid were produced in the upper aqueous phase. Thus, the dechlorination of PCDD/Fs and the oxidative degradation of the dechlorinated products seemed to take place simultaneously in the microcosm. Denaturing gel gradient electrophoresis and clone library analyses of PCR-amplified 16S rRNA genes from the microcosm showed that members of the phyla Firmicutes, Proteobacteria, and Bacteroidetes predominated. A significant number of Chloroflexi clones were also detected. Quantitative real-time PCR with specific primer sets showed that the 16S rRNA genes of a putative dechlorinator, "Dehalococcoides," and its relatives accounted for 0.1% of the total rRNA gene copies of the microcosm. Most of the clones thus obtained formed a cluster distinct from the typical "Dehalococcoides" group. Quinone profiling indicated that ubiquinones accounted for 18 to 25% of the total quinone content, suggesting the coexistence and activity of ubiquinone-containing aerobic bacteria. These results suggest that the apparent complete dechlorination of PCDD/Fs found in the microcosm was due to a combination of the dechlorinating activity of the "Dehalococcoides"-like organisms and the oxidative degradation of the dechlorinated products by aerobic bacteria with aromatic hydrocarbon dioxygenases.
Yoshida
Naoko
N
Department of Ecological Engineering, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580, Japan.
Takahashi
Nobutaka
N
Hiraishi
Akira
A
D000693:Anaerobiosis; D001420:Bacteria, Aerobic / Q000145:classification / Q000235:genetics / Q000378:metabolism; D001673:Biodegradation, Environmental; D002713:Chlorine / Q000378:metabolism*; D041862:Chloroflexi / Q000145:classification / Q000235:genetics / Q000378:metabolism; D003470:Culture Media; D004275:DNA, Ribosomal / Q000032:analysis; D004147:Dioxins / Q000378:metabolism*; D017753:Ecosystem; D020459:Genes, rRNA; D019015:Geologic Sediments / Q000382:microbiology; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S; D017422:Sequence Analysis, DNA; D014874:Water Pollutants, Chemical / Q000378:metabolism
D003470:Culture Media; D004275:DNA, Ribosomal; D004147:Dioxins; D012336:RNA, Ribosomal, 16S; D014874:Water Pollutants, Chemical; D002713:Chlorine