Microbial Characterization of Methanogenic and Iron-reducing Consortium in Reactors with Polychlorinated Biphenyls

Anaerobic co-digestion of three commercial bio-plastic bags with food waste: Effects on methane production and microbial community structure

The emergence of bioplastic bags as a replacement for traditional petroleum-based plastic bags is promising for their simultaneous anaerobic digestion with food waste. In this study, the degradation of three bioplastic bags is evaluated during anaerobic co-digestion with food waste under mesophilic/thermophilic conditions, and the results indicated PBAT/PLA/starch > PLA > PBAT for methane production rate. The PBAT/PLA/starch mixture produced 23.4 ml/g of methane at 55 °C, and the cumulative methane production increased by 28.4 % compared to the control. In addition, the lag time before methane production was reduced by one to four days when anaerobic co-digestion was performed under thermophilic conditions, and the conversion of the bioplastics improved by 9.11-11.2 %. Microscopy further showed obvious physical degradation of the PBAT/PLA/starch material. The FTIR analysis showed that the characteristic peaks of the material at 3320, 2957, and 934 cm^-1 decreased significantly after anaerobic fermentation. The biodegradability of the polymer decreased with an increase in the content of the crystalline area in the structure. The addition of a comonomer reduced the crystallinity of the polymer. In addition, the biodegradability was increased by adjusting the hydrolysis reaction and microbial activity of the polymer surface. An analysis of the structural features of the microbial communities revealed that Archaea exhibited different biodiversity at distinct temperatures. In particular, under thermophilic conditions, the relative abundance of Methanothermobacter was 56.0 %, and it plays an important role in the anaerobic degradation of PBAT/PLA/starch materials, while bacterial communities showed smaller differences. Overall, the bioplastic was able to be co-digested anaerobically with food waste to produce renewable energy. This study provides a plan for the practical application of biodegradable plastic bag collection for the combined treatment of food waste in anaerobic digesters. It provides a theoretical basis for modifications of bioplastic and domestication of anaerobic microorganisms.

Iron and total organic carbon shape the spatial distribution pattern of sediment Fe(III) reducing bacteria in a volcanic lake, NE China

Fe(III) reducing bacteria (FeRB) play a vital role in the biogeochemical cycle of Fe, C and N in nature. The volcanic lake can be considered as an ideal habitat for FeRB. Here, we investigated the diversity and spatial distribution of FeRB in sediments of Wenbo lake in Wudalianchi volcano based on culture-dependent and independent methods. A total of 28 isolates affiliated with the genera of Enterobacter, Bacillus, Pseudomonas and Clostridium were obtained from 18 sediment samples. We detected 783 operational taxonomic units (OTUs) belonged to FeRB using high high-throughput sequencing, and the dominant phyla were Proteobacteria (3.65%), Acidobacteria (0.29%), Firmicutes (10.78%). The representative FeRB genera such as Geobacter, Pseudomonas, Thiobacillus and Acinetobacter distributed widely in Wenbo lake. Results showed that the diversity and abundance of FeRB declined along the water-flow direction from Libo to Jingbo. In contrast, the FeRB diversity decreased and the FeRB abundance increased along with depth transect of sediments. It was found that the dominant phylum changed from Firmicutes to Proteobacteria along the water-flow direction, while changed from Proteobacteria to Firmicutes along with the depth of sediments. RDA indicated that the FeRB distribution were driven by soluble total iron, total organic carbon, Fe(II) and Fe(III). These will provide information for understanding the role of FeRB in the elements geochemical cycles in the volcanic environment.

Potential Role of Methanogens in Microbial Reductive Dechlorination of Organic Chlorinated Pollutants In Situ

Previous studies often attribute microbial reductive dechlorination to organohalide-respiring bacteria (OHRB) or cometabolic dechlorination bacteria (CORB). Even though methanogenesis frequently occurs during dechlorination of organic chlorinated pollutants (OCPs) in situ, the underestimated effect of methanogens and their interactions with dechlorinators remains unknown. We investigated the association between dechlorination and methanogenesis, as well as the performance of methanogens involved in reductive dechlorination, through the use of meta-analysis, incubation experiment, untargeted metabolomic analysis, and thermodynamic modeling approaches. The meta-analysis indicated that methanogenesis is largely synchronously associated with OCP dechlorination, that OHRB are not the sole degradation engineers that maintain OCP bioremediation, and that methanogens are fundamentally needed to sustain microenvironment functional balance. Laboratory results further confirmed that Methanosarcina barkeri (M. barkeri) promotes the dechlorination of γ-hexachlorocyclohexane (γ-HCH). Untargeted metabolomic analysis revealed that the application of γ-HCH upregulated the metabolic functioning of chlorocyclohexane and chlorobenzene degradation in M. barkeri, further confirming that M. barkeri potentially possesses an auxiliary dechlorination function. Finally, quantum analysis based on density functional theory (DFT) indicated that the methanogenic coenzyme F430 significantly reduces the activation barrier to dechlorination. Collectively, this work suggests that methanogens are highly involved in microbial reductive dechlorination at OCP-contaminated sites and may even directly favor OCP degradation.

Methane-associated micro-ecological processes crucially improve the self-purification of lindane-polluted paddy soil

Reductive dechlorination, an efficient pathway for complete removal of organic chlorinated pollutants (OCPs), is commonly reported to be coupled to oxidation of methane (CH₄) or methanogenesis in anaerobic environments. However, the relationship between dechlorination and CH₄-associated bioprocesses is unclear. Based on the hypothesis that CH₄ supplementation could facilitate OCP dechlorination, we investigated the role of CH₄-associated bioprocesses in the self-purification of flooded lindane-spiked paddy soils. Four treatments were conducted for up to 28 days: sterilized soil (S), sterilized soil + CH₄ (SC), non-sterilized soil (NS), and non-sterilized soil + CH₄ (NSC). Results indicated that both sterilization and addition of CH₄ promoted lindane degradation and CH₄ emissions in the flooded paddy soils. In the NS treatment, lindane had the lowest degradation rate when CH₄ emissions were barely detected; while in the SC treatment, lindane had the highest degradation rate when CH₄ achieved its highest emissions from anaerobic soil. Also, sterilization led to microbial diversity loss and functional recession, but increased ferrous ion [Fe(II)] concentrations compared to non-sterilized soils. Methanogenic communities and mcrA gene recovered faster than the majority of microorganisms (e.g., Fe bacteria, Bdellovibrionaceae, Rhizobiaceae, Dehalogenimonas) or functional genes (e.g., Dhc, Geo, narG, nirS). Collectively, we assume the enhanced removal of lindane may partly be due to both abiotic dechlorination promoted by chemical Fe redox processes and methanogenesis-derived biotic dechlorination. Revealing the coupling between dechlorination and CH₄-associated bioprocesses is helpful to resolve both pollution remediation and mitigation of CH₄ emissions in anaerobic contaminated sites.