Effects of elevated yet non-inhibitory levels of selenite on growth and gene expression of the methanogenic archaeon Methanococcus maripaludis JJ.

Selenium is an essential trace element in many organisms but becomes toxic at elevated concentrations. At moderately increased, non-lethal levels, selenite triggers both selenium utilization and stress responses in microorganisms. However, the thresholds of such responses in archaea remain poorly understood. Here, we investigated the effects of elevated yet non-inhibitory concentrations of selenite on growth and gene expression in the methanogenic archaeon Methanococcus maripaludis JJ. We observed no significant impact on growth rate or cell yield, even at 100 µM selenite. RNA sequencing and reverse transcription-quantitative polymerase chain reaction analyses revealed differential expression of genes involved in methanogenesis and transport systems, which may contribute to maintaining growth under elevated selenite. Our findings suggest that the transcriptional response to selenite in M. maripaludis is initiated at low concentrations (e.g., <1 µM) and remains saturated across a hundredfold range (up to 100 µM), without inducing stress responses or impairing growth.