Amplified selenite toxicity in methanogenic archaea mediated by cysteine

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The challenge of understanding the interaction between trace elements and microbial life is critical for assessing environmental and ecological impacts. Nevertheless, cysteine (Cys), a low molecular weight thiol substance prevalent in the ecosystem, is able to influence the fate of certain trace elements, which increases the complexity of the interaction between trace elements and microorganisms. Therefore, we chose Cys, selenite and the model methanogenic archaeon Methanosarcina acetivorans C2A as research targets, and comprehensively explored the intricate role of Cys in modulating the biological effects of selenite on M. acetivorans C2A in terms of population growth, methane production and oxidative stress. Our results demonstrate that Cys significantly exacerbates the inhibitory effects of selenite on growth and methane production in M. acetivorans C2A. This increased toxicity is linked to heightened membrane permeability and oxidative stress, with a marked upregulation in reactive oxygen species and changes in NADPH levels. Transcriptomic analysis reveals alterations in genes associated with transmembrane transport and methanogenesis. Intriguingly, we also observed a potential interaction between selenite and phosphate transmembrane transporters, suggesting a novel pathway for selenite entry into cells. These findings highlight the complex interplay between trace elements and microbial processes, with significant implications for understanding environmental risks and developing remediation strategies. • Cysteine enhanced selenite toxicity to methanogens. • Stabilization of protein structure in extracellular polymeric substance was destabilized. • ROS level was significantly elevated, causing strong oxidative stress. • Phosphate transporter underwent down-regulation, affecting the biological effects of selenite.