Exploring the variation of bacterial community and nitrogen transformation functional genes under the pressure of heavy metals in different coastal mariculture patterns

Cultivar-specific rhizosphere microbial community responses to cadmium-NaHCO3 stress in relation to cadmium accumulation in rice

Understanding the response of rhizosphere microbial communities to cadmium (Cd)-alkali stress from a cultivar-specific perspective is important for regulating Cd accumulation in rice. Pot experiments were conducted using low-Cd-accumulating Y15 and high-Cd-accumulating Y40, by addition of 0.0 %, 0.3 %, and 0.6 % NaHCO3 (A0, A1, and A2, respectively) to Cd-contaminated (0.62 mg/kg) soil. The plant Cd and soil DTPA-Cd decreased significantly with increasing NaHCO3 dose for Y15, but not for Y40. Cd-NaHCO3 stress reduced the richness and evenness of rhizosphere microbial communities, especially in A1 of Y15 and A2 of Y40. The Y15 rhizosphere shifted from the equal abundance of Proteobacteria and Firmicutes under A0 to the predominance of Proteobacteria and enriched with growth-promoting Alphaproteobacteria (Roseomonas, Brevundimonas), Cd-fixating Firmicute (Bacillus), and nitrogen-cycling Bdellovibrionota (Peredibacter) under A1 and A2. The Y40 rhizosphere contained comparable Proteobacteria and Firmicutes under A0 and A1; under A2, it was dominated by Proteobacteria and enriched with Cd-activating Bacteroidota (Barnesiella, Taibaiella), lignin-degrading Chloroflexi (Anaerolinea), and Cd-fixating or growth-promoting Gammaproteobacteria (Lysobacter, Pseudomonadales, Acinetobacter). The Y40 and Y15 rhizosphere exhibited laziness in multiple FAPROTAX functions, and were activated in 11 and 18 KGEE pathways including amino acid metabolism in A2 and A1, respectively. The results provide new insights into Cd-alkali tolerance in rice.

Impacts of aquaculture on nitrogen cycling and microbial community dynamics in coastal tidal flats

The expansion of aquaculture areas has encroached upon vast areas of coastal wetlands and introduced excessive nitrogen inputs, disrupting microbial communities and contributing to various environmental issues. However, investigations on how aquaculture affects microbial communities and nitrogen metabolism mechanisms in coastal tidal flats remain scarce. Hence, we explored the composition, diversity, and assembly processes of nitrogen-cycling (N-cycling) microbial communities in tidal flats in Jiangsu using metagenomic assembly methods. Our study further delved into the seasonal variations of these microbial characteristics to better explore the effects of seasonal changes in aquaculture areas on microbial community. Nitrogen metabolism-related processes and functional genes were identified through the KEGG and NCyc databases. The results revealed significant seasonal variation in the relative abundance and composition of microbial communities. Higher diversity was observed in winter, while the co-occurrence network of microbial communities was more complex in summer. Pseudomonadota emerged as the most abundant phylum in the N-cycling community. Furthermore, pH and NO3-N were identified as the primary factors influencing bacterial community composition, whereas NO2-N was more strongly associated with the N-cycling community. Regarding the nitrogen metabolism processes, nitrogen mineralization and nitrification were predominant in the tidal flat regions. NO2-N and NO3-N exhibited significant effects on several N-cycling functional genes (e.g., nirB, hao, and narG). Finally, neutral and null modeling analyses indicated that bacterial communities were predominantly shaped by stochastic processes, whereas N-cycling communities were largely driven by deterministic processes. These findings highlighted the significant role that aquaculture pollution plays in shaping the N-cycling communities in tidal flats. This underscored the importance of understanding microbial community dynamics and nitrogen metabolism in tidal flats to improve environmental management in coastal aquaculture areas.

Arsenic methylation and microbial communities in paddy soils under alternating anoxic and oxic conditions

Arsenic (As) methylation in soils affects the environmental behavior of As, excessive accumulation of dimethylarsenate (DMA) in rice plants leads to straighthead disease and a serious drop in crop yield. Understanding the mobility and transformation of methylated arsenic in redox-changing paddy fields is crucial for food security. Here, soils including un-arsenic contaminated (N-As), low-arsenic (L-As), medium-arsenic (M-As), and high-arsenic (H-As) soils were incubated under continuous anoxic, continuous oxic, and consecutive anoxic/oxic treatments respectively, to profile arsenic methylating process and microbial species involved in the As cycle. Under anoxic-oxic (A-O) treatment, methylated arsenic was significantly increased once oxygen was introduced into the incubation system. The methylated arsenic concentrations were up to 2-24 times higher than those in anoxic (A), oxic (O), and oxic-anoxic (O-A) treatments, under which arsenic was methylated slightly and then decreased in all four As concentration soils. In fact, the most plentiful arsenite S-adenosylmethionine methyltransferase genes (arsM) contributed to the increase in As methylation. Proteobacteria (40.8%-62.4%), Firmicutes (3.5%-15.7%), and Desulfobacterota (5.3%-13.3%) were the major microorganisms related to this process. These microbial increased markedly and played more important roles after oxygen was introduced, indicating that they were potential keystone microbial groups for As methylation in the alternating anoxic (flooding) and oxic (drainage) environment. The novel findings provided new insights into the reoxidation-driven arsenic methylation processes and the model could be used for further risk estimation in periodically flooded paddy fields.

Analysis of environmental biological effects and OBT accumulation potential of microalgae in freshwater systems exposed to tritium pollution

The ecological risk of tritiated wastewater into the environment has attracted much attention. Assessing the ecological risk of tritium-containing pollution is crucial by studying low-activity tritium exposure's environmental and biological effects on freshwater micro-environment and the enrichment potential of organically bound tritium (OBT) in microalgae and aquatic plants. The impact of tritium-contaminated wastewater on the microenvironment of freshwater systems was analyzed using microcosm experiments to simulate tritium pollution in freshwater systems. Low activity tritium pollution (105 Bq/L) induced differences in microbial abundance, with Proteobacteria, Bacteroidota, and Desulfobacterota occupying important ecological niches in the water system. Low activity tritium (105-107 Bq/L) did not affect the growth of microalgae and aquatic plants, but OBT was significantly enriched in microalgae and two aquatic plants (Pistia stratiotes, Spirodela polyrrhiza), with the enrichment coefficients of 2.08-3.39 and 1.71-2.13, respectively. At the transcriptional level, low-activity tritium (105 Bq/L) has the risk of interfering with gene expression in aquatic plants. Four dominant cyanobacterial strains (Leptolyngbya sp., Synechococcus elongatus, Nostoc sp., and Anabaena sp.) were isolated and demonstrated good environmental adaptability to tritium pollution. Environmental factors can modify the tritium accumulation potential in cyanobacteria and microalgae, theoretically enhancing food chain transfer.

Seasonal dynamics response mechanism of benthic microbial community to artificial reef habitats

Artificial reefs (ARs) have been globally deployed to enhance and restore coastal resource and ecosystems. Microorganisms play an essential role in marine ecosystems, while the knowledge regarding the impact of ARs on microecology is still limited, particularly data concerning the response of benthic microbial community to AR habitats. In this study, the seasonal dynamics of benthic microbial community in AR and adjacent non-artificial reef (NAR) areas surrounding Xiaoshi Island were investigated with high-throughput sequencing technology. The results revealed that the diversity and structure of microbial community between AR and NAR both displayed pronounced seasonal dynamics. There was a greater influence of season factors on microbial communities than that of habitat type. The microbial communities in AR and NAR habitats were characterized by a limited number of abundant taxa (ranging from 5 to 12 ASVs) with high relative abundance (8.35-25.53%) and numerous rare taxa (from 5994 to 12412 ASVs) with low relative abundance (11.91%-24.91%). Proteobacteria, Bacteroidota and Desulfobacterota were the common predominant phyla, with the relative abundances ranging from 50.94% to 76.76%. A total of 52 biomarkers were discovered, with 15, 4, 6, and 27 biomarkers identified in spring, summer, autumn and winter, respectively. Co-occurrence network analysis indicated that AR displayed a more complex interaction pattern and higher susceptibility to external disturbances. Furthermore, the neutral model and βNTI analyses revealed that the assembly of microbial communities in both AR and NAR is significantly influenced by stochastic processes. This study could provide valuable insights into the impact of ARs construction on the benthic ecosystems and would greatly facilitate the development and implementation of the future AR projects.

Arsenic removal in flue gas through anaerobic denitrification and sulfate reduction cocoupled arsenic oxidation

Arsenic in flue gas from municipal solid waste incineration can damage to human health and ecological environment. A sulfate-nitrate-reducing bioreactor (SNRBR) for flue gas arsenic removal was investigated. Arsenic removal efficiency attained 89.4%. An integrated metagenomic and metaproteomic investigation showed that three nitrate reductases (NapA, NapB and NarG), three sulfate reductases (Sat, AprAB and DsrAB), and arsenite oxidase (ArxA) regulated nitrate reduction, sulfate reduction and bacterial As(III)-oxidation, respectively. Citrobacter and Desulfobulbus could synthetically regulate the expression of arsenite-oxidizing gene, nitrate reductases and sulfate reducatases, which involved in As(III) oxidation, nitrate and sulfate reduction. A bacterial consortium containing Citrobacter, UG_Enterobacteriaceas, Desulfobulbus and Desulfovibrio could capable of simultaneously arsenic oxidation, sulfate reduction and denitrification. Anaerobic denitrification and sulfate reduction were cocoupled to arsenic oxidation. The biofilm was characterized by FTIR, XPS, XRD, EEM, and SEM. XRD and XPS spectra verified the formation of aarsenic species (As(V)) from flue gas As(III) conversion. Arsenic speciation in biofilms of SNRBR consisted of 77% residual arsenic, 15.9% organic matter-bound arsenic, and 4.3% strongly absorbed arsenic. Flue gas arsenic was bio-stabilized in the form of Fe-As-S and As-EPS through biodeposition, biosorption and biocomplexation. This provides a new way of flue gas arsenic removal using the sulfate-nitrate-reducing bioreactor.