Bacillus mycoides SeITE01 is an environmental isolate that transforms the oxyanion selenite (SeO32−) into the less bioavailable elemental selenium (Se⁰) forming biogenic selenium nanoparticles (Bio-SeNPs). In the present study, the reduction of sodium selenite (Na₂SeO₃) by SeITE01 strain and the effect of SeO32− exposure on the bacterial cells was examined through untargeted metabolomics. A time-course approach was used to monitor both cell pellet and cell free spent medium (referred as intracellular and extracellular, respectively) metabolites in SeITE01 cells treated or not with SeO32−. The results show substantial biochemical changes in SeITE01 cells when exposed to SeO32−. The initial uptake of SeO32− by SeITE01 cells (3h after inoculation) shows both an increase in intracellular levels of 4-hydroxybenzoate and indole-3-acetic acid, and an extracellular accumulation of guanosine, which are metabolites involved in general stress response adapting strategies. Proactive and defensive mechanisms against SeO32− are observed between the end of lag (12h) and beginning of exponential (18h) phases. Glutathione and N-acetyl-L-cysteine are thiol compounds that would be mainly involved in Painter-type reaction for the reduction and detoxification of SeO32− to Se⁰. In these growth stages, thiol metabolites perform a dual role, both acting against the toxic and harmful presence of the oxyanion and as substrate or reducing sources to scavenge ROS production. Moreover, detection of the amino acids L-threonine and ornithine suggests changes in membrane lipids. Starting from stationary phase (24 and 48h), metabolites related to the formation and release of SeNPs in the extracellular environment begin to be observed. 5-hydroxyindole acetate, D-[+]-glucosamine, 4-methyl-2-oxo pentanoic acid, and ethanolamine phosphate may represent signaling strategies following SeNPs release from the cytoplasmic compartment, with consequent damage to SeITE01 cell membranes. This is also accompanied by intracellular accumulation of trans-4-hydroxyproline and L-proline, which likely represent osmoprotectant activity. The identification of these metabolites suggests the activation of signaling strategies that would protect the bacterial cells from SeO32− toxicity while it is converting into SeNPs.

芽孢杆菌 SeITE01 是一种环境分离物，可转化氧阴离子亚硒酸盐 (硒32-) 进入生物利用度较低的元素硒 (Se ⁰ )，形成生物硒纳米颗粒 (Bio-SeNPs)。在本研究中，亚硒酸钠的还原（钠₂的SeO ₃通过SeITE01株）及效果硒32-通过非靶向代谢组学检查细菌细胞上的暴露。使用时程方法监测 SeITE01 细胞中的细胞沉淀和无细胞消耗培养基（分别称为细胞内和细胞外）代谢物硒32-. 结果显示，SeITE01 细胞在暴露于硒32-. 最初的吸收硒32-SeITE01 细胞（接种后 3 小时）显示 4-羟基苯甲酸和吲哚-3-乙酸的细胞内水平增加，以及鸟苷的细胞外积累，这些代谢物参与一般应激反应适应策略。主动防御机制硒32-在滞后 (12h) 结束和指数 (18h) 阶段开始之间观察到。谷胱甘肽和 N-乙酰基-L-半胱氨酸是硫醇化合物，主要参与画家型反应，以减少和解毒硒32-到硒⁰. 在这些生长阶段，硫醇代谢物具有双重作用，既可以对抗氧阴离子的有毒和有害存在，又可以作为底物或还原源来清除 ROS 的产生。此外，氨基酸 L-苏氨酸和鸟氨酸的检测表明膜脂的变化。从稳定期（24 和 48 小时）开始，开始观察到与细胞外环境中 SeNP 形成和释放相关的代谢物。5-羟基吲哚乙酸盐、D-[+]-葡萄糖胺、4-甲基-2-氧代戊酸和乙醇胺磷酸盐可能代表 SeNPs 从细胞质区室释放后的信号策略，从而对 SeITE01 细胞膜造成损害。这也伴随着反式 4-羟脯氨酸和 L-脯氨酸的细胞内积累，这可能代表了渗透保护活性。硒32- 转化为 SeNP 时的毒性。