Comparative molecular insights into selenium metabolism and nanoparticle biogenesis by Fructobacillus tropaeoli CRL2034 and Lactiplantibacillus plantarum CRL2051

Lactic acid bacteria (LAB) produce selenium-nanoparticles (SeNPs). However, the molecular and genetic mechanisms involved in these biotransformation processes are not yet fully understood. This work aimed to physicochemically characterize the SeNPs produced by Fructobacillus tropaeoli CRL2034 and Lactiplantibacillus plantarum CRL2051, study the differential expression of genes related to SeNPs synthesis and to analyze the relative expression of genes and proteins of selenized and non-selenized cells (control). The SeNPs produced by F. tropaeoli CRL2034 and L. plantarum CRL2051 showed an average size of 216.05 ± 19 and 286.14 ± 44 nm and ζ of –59.42 ± 5 and –56.77 ± 7 mV, respectively. The SeNPs produced showed spectroscopic signals compatible with Se–Se bonds and functional groups that confirm a biological coating composed of proteins, polysaccharides, and lipids. These SeNPs showed a dual structure, amorphous and crystalline. F. tropaeoli CRL2034 glutathione reductases and thioredoxin reductase could be involved in Se metabolism and SeNPs synthesis, while in L. plantarum CRL2051 a different strategy for SeNPs synthesis could be implicated. Selenized cells of L. plantarum differentially expressed proteins related to fatty acid metabolism and overexpressed a lysozyme/muramidase, which could be related to membrane and cell wall adaptation to Se-induced stress. Selenized cells of both strains repressed energy metabolism-related enzymes, which could be harmful to cell survival. The SeNPs produced by both LAB strains have suitable characteristics to be used in nutrition and/or biomedicinal applications. Moreover, the selenized LAB strains could have improved stress resistance properties and/or better adhesion to intestinal cells.