Mechanistic Insights into Nitrite Degradation by Metabolites of L. plantarum A50: An LC-MS-Based Untargeted Metabolomics Analysis

Abstract

Nitrites are universally acknowledged natural toxic substances that frequently lead to poisoning in humans and animals. During fermentation, certain microorganisms utilize a portion of the nitrogen element and reduce nitrates to nitrites through specific metabolic pathways. In this study, a highly effective lactic acid bacterial strain, Lactiplantibacillus plantarum A50, was isolated and screened from alfalfa silage for its remarkable ability to degrade nitrites. L. plantarum A50 exhibits exceptional nitrite removal capacity, with a degradation rate of 99.06% within 24 h. Furthermore, L. plantarum A50 demonstrates normal growth under pH values ranging from 4 to 9 and salt concentrations of 5%, displaying excellent tolerance to acidity, alkalinity, and salinity. Additionally, it undergoes fermentation using various carbon sources. Within the first 6–12 h of culture, L. plantarum A50 primarily achieves nitrite degradation through non-acidic processes, resulting in a degradation rate of 82.67% by the 12th hour. Moreover, the metabolites produced by L. plantarum A50 exhibit a synergistic interaction with acidity, leading to a nitrite degradation rate of 98.48% within 24 h. Notably, both L. plantarum A50 and MRS broth were found to degrade nitrites. Consequently, a non-targeted metabolomic analysis using LC-MS was conducted to identify 342 significantly different metabolites between L. plantarum A50 and MRS broth. Among these, lipids and lipid-like molecules, organic acids and derivatives, organic oxygen compounds, and organoheterocyclic compounds emerged as the main constituents. Lipids and lipid-like molecules, derivatives of glucose and galactose, amino acids and their derivatives, as well as organoheterocyclic compounds, are likely to play a role in nitrite elimination. Through the enrichment analysis of differential metabolic pathways using KEGG, nine distinct pathways were identified. These pathways provide essential nutrients, maintain cellular structure and function, participate in substance transport, regulate metabolic activities, and enhance resistance against pathogenic microorganisms in L. plantarum A50.