Effects of microplastics on cold seep sediment prokaryotic communities.

Cold seep sediments are an important reservoir of microplastics (MPs) whose impact on the structure and function of prokaryotic community is not well understood. In this study, the impact of 0.2% and 1% (w/w) polyethylene (PE), polystyrene (PS), and polypropylene (PP) MPs on the cold seep sediment prokaryotic community was investigated in a 120-day laboratory incubation experiment. The results revealed that exposure to MPs altered sedimentary chemical properties in a type- and concentration-dependent manner. Furthermore, MPs significantly altered the structure of bacterial community, with some MPs degradation-associated bacterial phyla significantly increasing (p < 0.05). However, in the case of archaea, the changes in the structure of microbial community were less pronounced (p > 0.05). Co-occurrence network analysis revealed that the addition of MPs reduced the network complexity, while PICRUSt2 and FAPROTAX analyses suggested that 0.2% PP and 1% PS MPs had the most significant effects on the nitrogen and carbon cycles (p < 0.05). Overall, this study provides new insights into the effects of MPs on the structure and function of microbial communities in cold seep sediments.

Response of sedimentary microbial community and antibiotic resistance genes to aged Micro(Nano)plastics exposure under high hydrostatic pressure.

Several studies reported that the presence of microplastics (MPs)/nanoplastics (NPs) in marine environments can alter microbial community and function. Yet, the impact of aged MPs/NPs on deep sea sedimentary ecosystems under high hydrostatic pressure remains insufficiently explored. Herein, the sedimentary microbial community composition, co-occurrence network, assembly, and transfer of antibiotic resistance genes (ARGs) in response to aged MPs/NPs were investigated. Compared with the control, NPs addition significantly reduced bacterial alpha diversity (p < 0.05), whereas MPs showed no significant impact (p > 0.05). Moreover, networks under NPs exhibited decreased complexity than that under MPs and the control, including edges, average degree, and the number of keystone. The assembly of the microbial community was primarily governed by stochastic processes, and aged MPs/NPs increased the importance of stochastic processes. Moreover, exposure to MPs/NPs for one month decreased the abundance of antibiotic resistance genes (ARGs) (from 94.8 to 36.2 TPM), while exposure for four months increased the abundance (from 40.6 to 88.1 TPM), and the shift of ARGs in sediment was driven by both functional modules and microbial community. This study is crucial for understanding the stress imposed by aged MPs/NPs on sedimentary ecosystems under high hydrostatic pressure.

The majority of microorganisms in gas hydrate-bearing subseafloor sediments ferment macromolecules.

BACKGROUND: Gas hydrate-bearing subseafloor sediments harbor a large number of microorganisms. Within these sediments, organic matter and upward-migrating methane are important carbon and energy sources fueling a light-independent biosphere. However, the type of metabolism that dominates the deep subseafloor of the gas hydrate zone is poorly constrained. Here we studied the microbial communities in gas hydrate-rich sediments up to 49 m below the seafloor recovered by drilling in the South China Sea. We focused on distinct geochemical conditions and performed metagenomic and metatranscriptomic analyses to characterize microbial communities and their role in carbon mineralization. RESULTS: Comparative microbial community analysis revealed that samples above and in sulfate-methane interface (SMI) zones were clearly distinguished from those below the SMI. Chloroflexota were most abundant above the SMI, whereas Caldatribacteriota dominated below the SMI. Verrucomicrobiota, Bathyarchaeia, and Hadarchaeota were similarly present in both types of sediment. The genomic inventory and transcriptional activity suggest an important role in the fermentation of macromolecules. In contrast, sulfate reducers and methanogens that catalyze the consumption or production of commonly observed chemical compounds in sediments are rare. Methanotrophs and alkanotrophs that anaerobically grow on alkanes were also identified to be at low abundances. The ANME-1 group actively thrived in or slightly below the current SMI. Members from Heimdallarchaeia were found to encode the potential for anaerobic oxidation of short-chain hydrocarbons. CONCLUSIONS: These findings indicate that the fermentation of macromolecules is the predominant energy source for microorganisms in deep subseafloor sediments that are experiencing upward methane fluxes. Video Abstract.