Environmental microbiology最新文献

Wastewater systems are important reservoirs of antibiotic resistance genes (ARGs), but the ecological and health risks of numerous latent ARGs (LARGs) remain unclear. In this study, we analysed 636 wastewater metagenomic samples from China and constructed a database containing 1587 LARGs. Across all environments, LARGs encoding serine-β-lactamases were the most abundant and prevalent. A comprehensive risk assessment, integrating host pathogenicity, gene mobility and environmental prevalence, was performed on 561 LARGs identified in metagenome-assembled genomes. Most LARGs exhibited low levels across all three dimensions, suggesting limited transmission risk. Nevertheless, 37 high-risk LARGs were identified, indicating non-negligible threats. Functional validation showed that the top three extremely high-risk LARGs significantly enhanced host resistance to ampicillin and ciprofloxacin when expressed in Escherichia coli, while AlphaFold3 revealed typical resistance protein folding, further supporting their functional activity. Horizontal gene transfer analysis indicated that these high-risk genes have disseminated from wastewater to natural water bodies such as rivers via plasmid-mediated mechanisms. Collectively, wastewater acts not only as an ‘accumulation pool’ for LARGs but also as a potential source releasing ‘super-risky’ resistance gene into the environment. Therefore, urgent efforts are needed to monitor and control these high-risk LARGs and their mobile genetic elements to block their environmental spread.

Two-component systems (TCS) play a vital role in bacterial adaptation to environmental stresses, including acid and metal toxicity. The ActJK system has been previously identified as a key regulator of acid tolerance in Sinorhizobium meliloti, a model organism for studying rhizobia-legume symbioses. Here, we expand the functional scope of ActJK, demonstrating its involvement in responses to copper and zinc stress. Using transcriptional fusion assays, we observed the ActJK's operon activation through degP1's upstream promoter region induction by Cu²⁺ and Zn²⁺ in a dose-dependent manner, a response absent in the ΔactJ mutant. Comparative proteomic analysis revealed distinct yet related overlapping regulatory pathways under Cu²⁺ and Zn²⁺ stress, with differentially expressed proteins suggesting convergence in efflux pump regulation and stress response mechanisms. The ΔactJ mutant displayed reduced tolerance to metal stress, impaired expression of metal detoxification genes, and altered antibiotic susceptibility profiles. Together, these findings highlight the intricate interplay between metal resistance and multidrug efflux systems in S. meliloti and underscore ActJK as a vital regulator integrating responses to environmental fluctuations. Understanding these regulatory mechanisms enhances our knowledge of bacterial survival in soil and rhizosphere under abiotic stress conditions and offers potential applications for optimising agricultural inoculants for acidic and metal-contaminated soils.

Lead [Pb(II)] and phenanthrene are major environmental co-pollutants that pose a serious threat to all life forms. The present study highlights the biofilm-associated stress responses in the marine filamentous fungus Aspergillus terreus HLP5 to various concentrations of Pb(II) and phenanthrene (25–500 ppm, 1:1 ratio). Highest biofilm formation shifted from 48 h in control to 72 h in presence of co-pollutants. A reduced surface-to-volume ratio in biofilm formed at 25–50 ppm Pb(II) + Phe indicated increased mycelial aggregation and compact architecture. The hyphal diameter increased with co-pollutant concentration. Gene expression analysis revealed downregulation of ags gene, whereas somA, medA, uge5, uge3, and gtb3 expression peaked at 72–96 h in 25–100 ppm of Pb(II) + Phe. Extracellular matrix (ECM) exhibited compositional and conformational modifications in polysaccharide and protein content. Major shifts were observed in functional groups corresponding to hydroxyl, Amide I-II, carboxyl, and phosphate moieties. Distinct peak at 8.36 ppm in ¹H NMR revealed phenanthrene-ECM interaction. A decrease in fluorescence intensity of tryptophan-like residues (290/355 nm) indicated ECM-co-pollutant binding. Upregulation of stress response genes (gst, acot2) and antioxidants like glutathione S-transferase, superoxide dismutase, and proline contributed to reduced ROS accumulation and redox homeostasis. These findings illustrated enhanced stress resilience of ECM-covered biofilm under co-pollutant stress.