Selenite bioremediation by food-grade probiotic Lactobacillus casei ATCC 393: insights from proteomics analysis

Microorganisms capable of converting toxic selenite into elemental selenium (Se0) are considered as an important and effective approach for bioremediation of Se contamination. In this study, we investigated the mechanism of reducing selenite to Se0 and forming Se nanoparticles (SeNPs) by food-grade probiotic Lactobacillus casei ATCC 393 (L. casei ATCC 393) through proteomics analysis. Proteomics analysis revealed that selenite induced a significant increase in the expression of glutaredoxin, oxidoreductase, and ATP binding cassette (ABC) transporter, which has the ability to transport glutathione (GSH) and selenite. Selenite treatment significantly increased the CydC and CydD (putative cysteine and glutathione importer, ABC transporter) mRNA expression level, GSH content and GSH reductase activity. Furthermore, supplementation with an additional GSH significantly increased the reduction rate of selenite, while GSH depletion significantly inhibited the reduction of selenite, indicating that GSH-mediated Painter-type reaction may be the main pathway of selenite reduction in L. casei ATCC 393. Moreover, nitrate reductase also participates in the reduction process of selenite, but it is not the primary factor.能够将有毒亚硒酸盐转化为单质硒（Se⁰）的微生物，被认为是硒污染生物修复的重要且高效途径。本研究通过蛋白质组学分析，探究了食品级益生菌干酪乳杆菌ATCC 393（L. casei ATCC 393）将亚硒酸盐还原为单质硒并合成硒纳米颗粒（SeNPs）的分子机制。蛋白质组学分析结果显示，亚硒酸盐可显著上调谷氧还蛋白、氧化还原酶以及ATP结合盒转运蛋白（ATP binding cassette transporter, ABC转运蛋白）的表达水平；该类转运蛋白能够介导谷胱甘肽（GSH）与亚硒酸盐的跨膜转运。亚硒酸盐处理可显著提升CydC与CydD（推定的半胱氨酸及谷胱甘肽导入型ABC转运蛋白）的mRNA表达水平、谷胱甘肽含量以及谷胱甘肽还原酶活性。此外，额外添加谷胱甘肽可显著提升亚硒酸盐的还原速率，而谷胱甘肽耗竭则会显著抑制亚硒酸盐的还原过程，这表明谷胱甘肽介导的潘特型（Painter-type）反应可能是干酪乳杆菌ATCC 393中亚硒酸盐还原的主要途径。此外，硝酸还原酶同样参与亚硒酸盐的还原过程，但并非该过程的核心影响因素。