Systems-level transcriptomic and physiological adaptation of Bacillus licheniformis BLN313 to selenite stress

Selenite (SeO₃^2-) is a highly toxic and mobile oxyanion that poses serious risks to environmental and biological systems. Microbial transformation of selenium plays a key role in determining its fate under contaminated conditions; however, the cellular regulatory processes governing microbial tolerance and selenium handling are not fully understood. Here, we employed an integrated approach to the transcriptome and biochemical method to study the cellular responses of Bacillus licheniformis BLN313 under graded selenite exposure. Growth dynamics and antioxidant enzyme activities showed a concentration-dependent stress response, consisting of high catalase, superoxide dismutase, and glutathione-associated activities, indicating activation of redox homeostasis mechanisms. RNA-sequencing analysis revealed widespread transcriptional reprogramming through oxidative stress responses, protein synthesis and translocation, membrane processes and central metabolism, suggesting coordinated cellular adaptation to selenium stress. Notably, selenite exposure caused repression of translational machinery coupled with up-regulation of stress-responsive and redox-related pathways, indicating an energy conservative strategy under toxic conditions. Integrative analysis supports the view that microbial selenium tolerance is controlled by regulated physiological responses and not solely by passive detoxification. Exploratory protein enrichment analysis implicated Sec translocon components as candidate stress-responsive proteins, converging with transcriptomic evidence. These findings provide systems-level mechanistic insight into microbial selenite tolerance with implications for bioremediation of selenium-contaminated environments.