Isolation of a novel Lactiplantibacillus plantarum strain resistant to nitrite stress and its transcriptome analysis

Nitric oxide (NO) is a reactive nitrogen species (RNS) that plays a vital role in regulating inflammatory processes. Under abnormal conditions, excessive NO levels can promote the oxidation of cellular components, which may cause or exacerbate diseases such as hypertension, cardiovascular dysfunction, and inflammatory bowel disease (IBD). Previous studies have shown that reducing NO levels in the lumen can attenuate the clinical symptoms of IBD. Thus, we aimed to identify bacteria that can reduce RNS and that can be used as valuable probiotics. In this study, we isolated bacteria resistant to nitrite stress from human feces and used 16S and whole-genome sequencing to identify them as Lactiplantibacillus plantarum LP7 (LP7). The ability to survive at high nitrite levels and to decrease them was greater in the LP7 strain than in the reference strain L. plantarum ATCC14917 (ATCC14917). To characterize the LP7 genome in more detail, we performed a comparative genome analysis. However, the unique genes that directly confer the ability to withstand nitrite stress were not present in the LP7 genome. Furthermore, we performed transcriptomic analysis of LP7 and ATCC14917 cells treated with nitrite. We found that the expression levels of genes involved in the cell division process were induced in LP7, which showed a more regular rod-shape than ATCC14917. This could explain why LP7 can survive better than ATCC14917 under nitrite stress. Based on its ability to survive better in nitrite stress and decrease nitrite concentration, we suggest that LP7 could be a valuable probiotic strain.