Microplastics increase the microbial functional potential of greenhouse gas emissions and water pollution in a freshwater lake: A metagenomic study.

Aquatic ecosystems are being increasingly polluted by microplastics (MPs), which calls for an understanding of how MPs affect microbially driven biogenic element cycling in water environments. A 28-day incubation experiment was conducted using freshwater lake water added with three polymer types of MPs (i.e., polyethylene, polypropylene, polystyrene) separately or in combination at a concentration of 1 items/L. The effects of various MPs on microbial communities and functional genes related to carbon, nitrogen, phosphorus, and sulfur cycling were analyzed using metagenomics. Results showed that Sphingomonas and Novosphingobium, which were indicator taxa (genus level) in the polyethylene treatment group, made the largest functional contribution to biogenic element cycling. Following the addition of MPs, the relative abundances of genes related to methane oxidation (e.g., hdrD, frhB, accAB) and denitrification (napABC, nirK, norB) increased. These changes were accompanied by increased relative abundances of genes involved in organic phosphorus mineralization (e.g., phoAD) and sulfate reduction (cysHIJ), as well as decreased relative abundances of genes involved in phosphate transport (phnCDE) and the SOX system. Findings of this study underscore that MPs, especially polyethylene, increase the potential of greenhouse gas emissions (CO2, N2O) and water pollution (PO43-, H2S) in freshwater lakes at the functional gene level.

Microbial pathways in the coupling of iron, sulfur, and phosphorus cycles at the sediment-water interface of a river system: An in situ study involving the DGT technique.

It is imperative to solve the problem of endogenous phosphorus (P) release from sediments in the governance of natural water bodies. Deciphering P migration and transformation patterns that are coupled to iron (Fe) and sulfur (S) cycling at the sediment-water interface (SWI) is the key to understanding the mechanisms underlying endogenous P release. In the present study, we deployed diffusive gradients in thin films (DGT) probes in situ at the SWI in Fuyang River, Hebei Province, China. When the probes were retrieved, the surrounding sediments were synchronously sampled. We analyzed the longitudinal spatiotemporal distribution of Fe, S, and P at the SWI. We also explored how functional bacterial community diversity was associated with the coupling reactions of Fe, S, and P as well as endogenous P release from sediments at the functional gene level. The results showed that labile Fe, S, and P occurred at low concentrations in sediments 0-2 cm below the SWI, while they were enriched in sediments at depths of 4-8 cm. The longitudinal distribution of different labile elements exhibited greater differences between October and February than regional differences, with higher concentrations at downstream locations than upstream locations. In February, Fe/Al-bound P and sulfide (S2-) concentrations increased in sediments compared with those in October owing to an increase in the relative abundances of dominant genera among P-mineralizing bacteria and sulfate-reducing bacteria. As a result, Fe in Fe-bound P precipitated as FeS2, which induced P remobilization and release into the overlying water. The spatiotemporal distribution patterns of functional genes related to P (phoD and ppk) and S (aprA) transformation were consistent with those of labile P and S, which strongly suggests that microorganisms played a role in driving and regulating the coupled cycling of P and S at the SWI.

Micro-pressure promotes endogenous phosphorus release in a deep reservoir by favouring microbial phosphate mineralisation and solubilisation coupled with sulphate reduction.

Deep reservoirs vary in their hydrostatic pressure owing to artificial water level control. The potential migration of phosphorus (P) in reservoir sediments raises the risk of harmful algal blooms. To ascertain the mechanisms of endogenous P release in reservoirs, we characterised aquatic microbial communities associated with coupled iron (Fe), P and sulphur (S) cycling at the sediment-water interface. The responses of microbial communities to hydrostatic pressures of 0.2-0.7 mega pascals (MPa; that is, micro-pressures) were investigated through a 30-day simulation experiment. Our findings unravelled a potential mechanism that micro-pressure enhanced the solubilisation of Fe/aluminium (Al)-bound P caused by microbially-driven sulphate reduction, leading to endogenous P release in the deep reservoir. Although the vertical distribution of labile Fe was not affected by pressure changes, we did observe Fe resupply at sediment depths of 2-5 cm. Metagenomic analysis revealed increased abundances of functional genes for P mineralisation (phoD, phoA), P solubilisation (pqqC, ppx-gppA) and sulphate reduction (cysD, cysC) in sediments subjected to micro-pressure, which contrasted with the pattern of S oxidation gene (soxB). There was a tight connection between P and S cycling-related microbial communities, based on significant positive correlations between labile element (P and S) concentrations and functional gene (phoD, cysD) abundances. This provided strong support that Fe-P-S coupling processes were governed by micro-pressure through modulation of P and S cycling-related microbial functions. Key taxa involved in P and S cycling (for example, Bradyrhizobium, Methyloceanibacter) positively responded to micro-pressure and as such, indirectly drove P release from sediments by facilitating P mineralisation and solubilisation coupled with sulphate reduction.

Hydrostatic pressure drives microbe-mediated biodegradation of microplastics in surface sediments of deep reservoirs: Novel findings from hydrostatic pressure simulation experiments.

Microplastics originate from the physical, chemical, or biological degradation of plastics in the environment. Once ingested by organisms at the bottom of the food chain, microplastics are passed on to organisms at higher trophic levels, posing a threat to human health. The distribution of microplastics and the metabolic pathways involved in their microbial degradation in surface sediments of drinking water reservoirs are still poorly understood. This study analyzed the occurrence patterns of microplastics and microbial community structure associated with microplastic biodegradation in surface sediments from a deep reservoir at various hydrostatic pressures. Based on the results of Fourier-transform and laser direct infrared spectroscopy, elevating the pressure resulted in altered sizes and shapes of microplastics in sediment samples with the presence of microorganisms. The influence of hydrostatic pressure on small-sized microplastics (20-500 µm) was pronounced. For instance, high pressure accelerated the breakdown of fibers, pellets, and fragments into smaller-sized microplastics. In particular, the mean size of polyethylene terephthalate microplastics decreased from 425.78 µm at atmospheric pressure to 366.62 µm at 0.7 Mpa. Metagenomic analysis revealed an increase in the relative abundances of plastic-degrading genera, such as Rhodococcus, Flavobacterium, and Aspergillus, in response to elevated pressures. Eight functional genes for biodegradation of polystyrene, polyethylene, and polyethylene terephthalate microplastics were annotated, including paaK, ladA, tphA3. Of these, tphA3 gene abundance was negatively influenced by hydrostatic pressure, providing direct evidence for the pathway by which microbial metabolism of polyethylene terephthalate led to decreased microplastic size under high pressure conditions. This study presents novel insights into hydrostatic pressure-driven microbial community structure, functional gene abundance, and key metabolic pathways associated with biodegradation of microplastics in reservoir sediments.