Population dynamics of polychlorinated biphenyl-dechlorinating microorganisms in contaminated sediments

Abstract

The growth dynamics of polychlorinated biphenyl (PCB)-dechlorinating microorganisms were determined for the first time, along with those of sulfate reducers and methanogens, by using the most-probable-number technique. The time course of Aroclor 1248 dechlorination mirrored the growth of dechlorinators; dechlorination ensued when the dechlorinating population increased by 2 orders of magnitude from 2.5 ؋ 10 5 to 4.6 ؋ 10 7 cells g of sediment ؊1 , at a specific growth rate of 6.7 day ؊1 between 2 and 6 weeks. During this period, PCB-dechlorinating microorganisms dechlorinated Aroclor 1248 at a rate of 3.9 ؋ 10 ؊8 mol of Cl g of sediment ؊1 day ؊1 , reducing the average number of Cl molecules per biphenyl from 3.9 to 2.8. The growth yield was 4.2 ؋ 10 13 cells mol of Cl dechlorinated ؊1 . Once dechlorination reached a plateau, after 6 weeks, the number of dechlorinators began to decrease. On the other hand, dechlorinators inoculated into PCB-free sediments decreased over time from their initial level, suggesting that PCBs are required for their selective enrichment. The numbers of sulfate reducers and methanogens increased in both PCB-free and contaminated sediments, showing little difference between them. The maximum population size of sulfate reducers was about an order of magnitude higher than that of dechlorinators, whereas that of methanogens was slightly less. Unlike those of dechlorinators, however, numbers of both sulfate reducers and methanogens remained high even when dechlorination ceased. The results of this study imply that PCB concentrations may have to exceed a certain threshold to maintain the growth of PCB dechlorinators.

Reductive dechlorination of polychlorinated biphenyls: Interactions of dechlorinating microorganisms with methanogens and sulfate reducers

“…Chem. 18, 1999 2701 that observed in BES-free sediments, the pattern with higher dilution inocula was similar to that observed in BES-amended sediments [19]. These results suggest that the methanogenic population involved in dechlorination may have a low affinity for the PCB mixture and that its size is relatively small.…”

“…1). The fact that the number of sulfate reducers in inhibitor-free cultures was about one to two orders of magnitude higher than those of methanogens or dechlorinators indicates that sulfate reducers were a dominant population under these experimental conditions, as was the case in our earlier study [14]. Neither dechlorination nor growth of dechlorinators was observed in sediments amended with both inhibitors.…”

“…3). [All MPN numbers in the previous study (Kim and Rhee [14]) were overestimated by an order of magnitude because of a calculation error. ]…”

“…After phase separation, the hexane layer was transferred into a flask containing sodium sulfate in order to remove any residual water. Polychlorinated biphenyls in the MPN test vials were extracted twice, first with acetone-hexane (1:1, v/v) by shaking on an orbital shaker overnight and then by shaking for 4 h with hexane [14].…”

Effect of aroclor 1248 concentration on the rate and extent of polychlorinated biphenyl dechlorination

“…Therefore, if biomass was also proportional to PCB concentrations, the linear pattern could drastically change. Using the most-probable-number technique, we recently demonstrated that the growth of PCB-dechlorinating microorganisms requires the presence of PCBs [23]. This finding suggests that the biomass of dechlorinators may also vary with PCB concentration.…”