| Pentachlorophenol (PCP, C6Cl5OH) is a common kind of ionizable hydrophobic organic contaminants which had been extensively used in the world as an important component of pesticide, herbicide, antiseptic and wood preservatives. In the1970s, PCP was popularly used in China in fighting against snail fever. Although pentachlorophenol had been banned from production and use in the1980s, due to its strong ability of resisting degradation, its impact on the environment will also continue for quite a long time.In this study, two kinds of different anaerobic microbial communities, the PCP domesticated consortium and the iron reducing consortium, were enriched by serial transfers from a paddy soil. The reductive transformation of pentachlorophenol (PCP) by these two communities was investigated in presence of three different kinds of iron oxides(HFO, γ-FeOOH.α-FeOOH). The influence of extraneous electron donor (NaAc) and electronic receptor (NaNO3) on this process was also evaluated. Then, DGGE and qPCR molecular methods were used to determine the variation in microbial community structures, for illustrating the microbial mechanisms involved underpinning the reductive transformation of PCP coupled with iron reduction. The main results of the study are as follows:(1) The microorganisms in bacterial suspension played an important role in PCP transformation, irrespective of consortium type. The average PCP reduction rate in treatments with iron oxides was significantly higher than that without iron oxides (p<0.05), indicated that the presence of iron oxides can promote the reduction of PCP in anaerobic conditions. Meanwhile, in the absence of iron oxides, the transformation rates of PCP in different bacterial suspension was in the order of PCP domesticated consortium> iron reducing consortium; while this order was opposite in the presence of iron oxides. This suggested that the reductive transformation of PCP by iron reducing consortium could be facilitated when coupling with the reduction of iron oxides.(2) The addition of10mmol L-1NaAc or5mmol L-1NaNO3inhibited the reduction of PCP and iron oxides. NaAc might be used as a carbon source instead of electron donor by microorganisms. NaNO3might affect the reduction of PCP through the following several aspects:compete with PCP for electrons; compete with iron oxide for electrons and then decrease the amount of active iron species; compete with PCP for active sites on the surface of iron oxides.(3) The DGGE profiles showed that the microbial community structures were different between PCP domesticated and iron reducing consortium, This was coincident with the cluster analysis, which showed that these two consortiums belonged to two different microbial categories. The results testified that through different directional domestication, different microbial communities could be enriched and obtained with different specific environmental function. As suggested by DGGE profiles, there were some specific microorganisms enriched during the incubation. The specific bands (in total of16) that predominated in DGGE profiles or were different from others were incised, and then cloned and sequenced. The results showed that11of them belonged to Firmicutes and the others were Proteobacteria.(4) In both suspension systems of consortiums, the16s rRNA gene copy numbers of Geobacteraceae increased first then decreased, which showed the same variation trend with the reduction of iron oxides. Correlation analysis also showed that the adsorbed Fe(II) is significantly related to the copy numbers of Geobacteraceae gene. This indicated that Geobacteraceae might be involved in the reduction process of iron oxides. As for reductive dechlorinating microorganisms Dehalobacter and Desulfitobacterium, their amounts were below the limit of detection. This indicated that in the two bacterial consortium suspension systems, the reductive transformation of PCP was achieved not in a direct way of microbial degradation, but mainly in an indirect way through coupling with Fe (III) reduction. |
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