How wastewater with different nutrient levels influences microbial degradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in anaerobic sediments

Insight into microbial degradation of hexabromocyclododecane (HBCD) in lake sediments under different hydrodynamic conditions

Hexabromocyclododecane (HBCD), an emerging persistent organic pollutant, has been widely detected in aquatic ecosystems with various hydrodynamic conditions, however, the effects of hydrodynamic changes on microbial degradation of HBCD in aquatic sediment remains unclear. Here, we conducted an annular flume experiment to characterize variation in HBCD removal from contaminated sediment under three hydrodynamic conditions with different flow velocities, as well as clarify the underlying microbial mechanisms. We detected significant HBCD removal and bromine ion generation in all contaminated sediments, and microbial reduction debromination was an important process for HBCD removal. At the end of the 49-day experiment, both HBCD removal percentage and the bromine ion concentration were significantly lower under dynamic water condition with higher sediment redox potential, compared with static water conditions. The dynamic water conditions resulted a relatively high sediment redox potential and decreased the iron reduction rate and the abundance of organohalide-respiring bacteria (OHRB) in the genera Geobatcer, Dehalogenimonas, Dehalobacter, and Dehalococcoide, which reduced the microbial degradation of HBCD in contaminated sediments. The community composition of both total bacteria and OHRB also differed significantly among hydrodynamic conditions. Some bacterial groups with HBCD degradation abilities such as Pseudomonas and Sulfuricurvum were less abundant under dynamic water conditions, and the HBCD degradation efficiencies were lower. These findings enhance our understanding of the bioremediation potential of HBCD-contaminated sediments in different hydrodynamic areas.

Microbial and abiotic factors of flooded soil that affect redox biodegradation of lindane

Pollution induces pressure to soil microorganism; and conversely, the degradation of pollutants is reported largely regulated by the soil microbiome assembly in situ. However, the specific-dependent core taxa of degraders were barely confirmed, which is not conducive to improving the soil remediation strategy. Taking pollution of a typical organochlorine pesticide (OCP), lindane, as an example, we explored the microbial community assembly in flooded soils and simultaneously quantified the corresponding dynamics of typical soil redox processes. Contrasting initial status of microbial diversity was set up by gamma irradiation or not, with additives (acetate, NaNO_3, acetate + NaNO₃) capable of modifying microbial growth employed simultaneously. Microorganism under lindane stress was reflected by microbial adaptability within complex co-occurrence networks, wherein some environment-dependent core taxa (e.g., Clostridia, Bacteroidia, Bacilli) were highly resilient to pollution and sterilization disturbances. Lindane had higher degradation rate in irradiated soil (0.96 mg kg^-1 d^-1) than non-irradiated soil (0.83 mg kg^-1 d^-1). In non-irradiated soil, addition of acetate promoted lindane degradation and methanogenesis, whereas nitrate inhibited lindane degradation but promoted denitrification. No significant differences in lindane degradation were observed in irradiated soils, which exhibited low-diversity microbiomes in parallel to stronger Fe reduction and methanogenesis. The varied corresponding trigger effects on soil redox processes are likely due to differences of soil microbiome, specifically, deterministic or stochastic assembly, in response to pollution stress under high or low initial microbial diversity conditions. Our results improve the knowledge of the adaptability of disturbed microbiomes and their feedback on microbial functional development in OCP-polluted soils, achieving for a more reliable understanding with respect to the ecological risk of soils resided with OCPs under the fact of global microbial diversity loss.

Anaerobic Degradation of Propanil in Soil and Sediment Using Mixed Bacterial Culture

The widespread use of the herbicide, propanil, causes severe environmental problems. In this study, the effects of propanil on the bacterial community in a sediment slurry were determined. Moreover, the degradation of the herbicide by pure and mixed cultures was first conducted under anaerobic conditions. The results showed that propanil caused significant changes in the bacterial community under anaerobic conditions. Four bacterial strains, i.e., Geobacter sp. Pr-1, Paracoccus denitrificans Pr-2, Pseudomonas sp. Pr-3, and Rhodococcus sp. Pr-4, isolated from the an enrichment sediment slurry were the first pure cultures that degraded propanil and 3,4-dichloroaniline (3,4-DCA) under anaerobic conditions. Some individual isolates showed the slow degradation of propanil and 3,4-DCA, but the mixture of the four strains increased the degradation rates of both compounds. The mixed culture of these isolates transformed more than 90% of propanil within 10 days in liquid media with the amendment of dextrose, glucose, or acetate. The determination of degradation pathway showed that propanil was transformed to 3,4-DCA and some other products before degrading completely. This study provides valuable information on the effects of propanil on the bacterial community and the synergistic degradation of propanil under anaerobic conditions.

The investigation of bioremediation potential of Bacillus subtilis and B. thuringiensis isolates under controlled conditions in freshwater

Bioremediation is widely used to remove water pollution as environmentally friendly smart solutions. In this study, Bacillus isolates were investigated in terms of the effectiveness of single and multiple cultures in eliminating aquatic pollution related to aquaculture activities. In the established experimental setups, the environments where Bacillus isolates were inoculated with single and multiple cultures at 1 × 10⁷ CFU/mL were evaluated comparatively with control groups without these isolates, and total aerobic mesophilic bacterial counts were performed in the petri dish by inoculation method. At the end of the 6 days of the experiment, in the environment in which single and multiple cultures of Bacillus isolates were presented with 17-20 ± 0.05 °C temperature and 5.1-8.1 pH 2-4.6 mg/l dissolved oxygen values (O₂), 2% increase in total phosphorus (TP) value was observed. On the other hand, 4% removal of Ammonia-nitrogen (NH₃-N), 80% removal of Nitrite-nitrogen (NO₂-N), and 100% removal of Nitrate-nitrogen (NO₃-N) were observed. In the changes in heavy metal concentrations, the removal of Ni, Cr, Se, Al, Cd, Mn, Fe, and B was observed from highest to lowest as 57%, 50%, 50%, 43%, 40%, 23%, 5%, and 2%, respectively. It also has been seen that B. thuringiensis isolate was observed to be more effective than B. subtilis in metal removal.

Nanoscale zero-valent iron reduction coupled with anaerobic dechlorination to degrade hexachlorocyclohexane isomers in historically contaminated soil

Hexachlorocyclohexane (HCH) isomers pose potential threats to the environment and to public health due to their persistence and high toxicity. In this study, nanoscale zero-valent iron (nZVI) coupled with microbial degradation by indigenous microorganisms with and without biostimulation was employed to remediate soils highly polluted with HCH. The degradation efficiency of total HCHs in both the "nZVI-only" and "Non-amendment" treatments was approximately 50 %, while in the treatment amended with nZVI and acetate, 85 % of total HCHs was removed. Addition of nZVI and acetate resulted in enrichment of anaerobic microorganisms. The results of quantitative PCR (qPCR) and 16S rRNA gene amplicon sequencing revealed that Desulfotomaculum, Dehalobacter, Geobacter, and Desulfuromonas likely contributed to the depletion of HCH isomers. Moreover, some abiotic factors also favored this removal process, including pH, and the generation of iron sulfides as revealed by the result of Mössbauer spectrometer analysis. Our research provides an improved remediation strategy for soils polluted with HCH isomers and an understanding of the synergistic effect of nZVI and indigenous microorganisms.