A microbially facilitated approach was developed to degrade 2, 2′, 4, 4′-tetrabrominated diphenyl ether (BDE-47). This approach consisted of biological production of Fe(II) and H₂O₂ by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 during the repetitive anoxic/oxic cycles and abiotic production of hydroxyl radical (HO●) with the biologically produced Fe(II) and H₂O₂ via Fenton reaction. Under the condition tested, BDE-47 did not inhibit the growth of S. oneidensis MR-1. Water soluble Fe(III)-citrate and the solid minerals ferrihydrite [Fe(III)₂O₃•0.5H₂O] and goethite [Fe(III)OOH] were tested in this study. Under anoxic condition, the amounts of Fe(II) produced by S. oneidensis MR-1 varied among the Fe(III)s tested, which decreased in the order of Fe(III)-citrate > ferrihydrite > goethite. Under subsequent oxic condition, H₂O₂ was produced via O₂ reduction by S. oneidensis MR-1. The amounts of H₂O₂ detected also varied, which decreased in the order of the reactions with Fe(III)-citrate > goethite > ferrihydrite. S. oneidensis MR-1 maintained its ability to produce Fe(II) and H₂O₂ for up to seven anoxic/oxic cycles. At each end of anoxic/oxic cycle, HO● was detected. The amount of HO● produced decreased in the order of the reactions with ferrihydrite > goethite > Fe(III)-citrate, which was opposite to that of H₂O₂ detected. Compared to the controls without HO●, the amounts of BDE-47 in the reactions with HO● decreased. The more HO● in the reaction, the less amount of BDE-47 detected. Furthermore, no BDE-47 degradation was observed when HO● was scavenged or ferrihydrite was either omitted or replaced by nitrate. Finally, identification of degradation products, such as hydroxylated BDE-47 and trisBDE, dibromophenol and monobromophenol, suggested that OH-addition and Br-substitution by HO● were the main mechanisms for degrading BDE-47. Collectively, all these results demonstrated for the first time that the Fenton reaction driven by S. oneidensis MR-1 degraded BDE-47 effectively.

With the burst of silver nanoparticles (AgNPs) applications, their potential entry into the environment has attracted increasing concern. To date, researches about the impacts of AgNPs on microbial communities have been scarcely conducted in the brackish waters. Here, the effects of interactions of AgNPs and Ag⁺ (as a positive control) with dissolved oxygen on natural brackish water microbial communities were investigated for 30 d. The introduction of AgNPs and Ag⁺ in natural brackish waters resulted in distinct bacterial community composition and structure as well as reduction of the richness and diversity, effects that were not eliminated completely during the tested periods. Anoxic conditions could attenuate the effects of AgNPs and Ag⁺ on the community, and dissolved oxygen made more contributions to community compositions for short-term exposure. High doses of AgNPs had more pronounced long-term impacts than Ag⁺ amendment. Compared with the controls, two general AgNP and Ag⁺ responses, namely, sensitivity and resistance, were observed. Sensitive species mainly included those of the genera Synechococcus and unclassified_f_Rhodobacteraceae, while resistant species mostly belonged to the phylum Bacteroidetes and participated in carbon metabolic processes. Our results indicated that the microbial communities that were involved in nutrient cycles (such as carbon, nitrogen, and sulfide) and photoautotrophic bacteria that contained bacteriochlorophyll were adversely affected by AgNPs and Ag⁺. In addition, dissolved oxygen could further change the microbial communities. These results implied that under different oxygen conditions AgNPs possibly resulted in varying microbial survival strategies and affected the biogeochemical cycling of nutrients in natural brackish waters.

Bacteria with arsenate-reducing (ars) and arsenite-oxidizing (aio) genes usually co-exist in aerobic environments, but their contrast impacts on arsenic (As) speciation and mobility remain unclear. To identify which kind of bacteria dominate As speciation under oxic conditions, we studied the biotransformation of adsorbed As on goethite in the co-existence of Pantoea sp. IMH with ars gene and Achromobacter sp. SY8 with aio gene. The incubation results show that SY8 dominated the dissolved As speciation as As(V), even though aio exhibited nearly 5 folds lower transcription levels than ars in IMH. Nevertheless, our XANES results suggest that SY8 showed a negligible effect on solid-bound As speciation whereas IMH reduced adsorbed As(V) to As(III). The change in As speciation on goethite surfaces led to a partial As structural change from bidentate corner-sharing to monodentate corner-sharing as evidenced by our EXFAS analysis. Our Mössbauer spectroscopic results suggest that the incubation with SY8 reduced the degree of crystallinity of goethite, and the reduced crystallinity can be partly compensated by IMH. The changes in As adsorption structure and in goethite crystallinity had a negligible effect on As release. The insights gained from this study improve our understanding of biotransformation of As in aerobic environment.

Fluorotelomer compounds in landfill leachate can undergo biotransformation under aerobic conditions and act as a secondary source of perfluorocarboxylic acids (PFCAs) to the environment. Very little is known about the role of various microbial communities towards fluorotelomer compounds biotransformation. Using an inoculum prepared from the sediment of a leachate collection ditch, 6:2 fluorotelomer sulfonate (6:2 FTS) biotransformation experiments were carried out. Specific substrates (i.e., glucose, ammonia) and ammonia-oxidizing inhibitor (allylthiourea) were used to produce two experimental runs with heterotrophic (HET) growth only and heterotrophic with ammonia-oxidizing and nitrite- oxidizing bacteria (HET + AOB + NOB). After 10 days, ∼20% of the spiked 6:2 FTS removal was observed in HET + AOB + NOB, compared to ∼7% under HET condition. Higher 6:2 FTS removal in HET + AOB + NOB likely resulted from ammonia monooxygenase enzyme that catalyzes the first step of ammonia oxidation. The HET + AOB + NOB condition also showed higher PFCA (C4–C6) formation (∼2% of initially spiked 6:2 FTS), possibly due to higher overall bioactivity. Microbial community analysis through 16s rRNA sequencing confirmed that Proteobacteria and Bacteroidetes were the most abundant phyla (>75% relative abundance) under all experimental conditions. High abundance of Actinobacteria (>17%) was observed under the HET + AOB + NOB condition on day 7. Since Actinobacteria can synthesize a wide range of enzymes including monooxygenases, they likely play an important role in 6:2 FTS biotransformation and PFCA production.

The MeHg content in the reed wetland soil of Liaohe was studied by the indoor-simulated constant temperature culture method. Under different aerobic and anaerobic conditions, the flooding salinity (CK, 0.5%, 1.0%, 1.5%, 2.0%) changes relationship whether SRB plays a leading role in the formation of MeHg. The results showed that under aerobic conditions, the content of MeHg in the surface layer and the bottom layer showed a trend of decreasing first and then increasing with the increase of culture time. Both of them have a lower MeHg content when the flooding salinity is 2.0%. The number of SRB bacteria showed a trend of “upgrading-depleting” with the increase of flooding salinity. Under anaerobic conditions, the MeHg content of surface and bottom soil changed slowly in the early stage of culture (the first 10 days), and the MeHg content increased rapidly after 15 days of culture, and decreased significantly on the 25th day. The number of SRB bacteria showed a trend of “depleting-upgrading” as the flooding salinity increased. Linear fitting showed that there was no obvious linear relationship between the change of MeHg content in soil and the number of SRB bacteria, and other microorganisms may play a role in methylation of mercury. Under anaerobic conditions, MeHg content in surface soil was significantly positively correlated with organic matter (p < 0.01), but negatively correlated with total mercury (p < 0.05). The mercury methylation process is affected by many environmental factors, and the mechanism of mercury methylation in different environments is different.