Potential mechanism of nitrite degradation by Lactobacillus fermentum RC4 based on proteomic analysis

Nitrite helps meat products retain colour and prevents decay, but excessive intake can be carcinogenic. To investigate the mechanism of nitrite degradation by lactic acid bacteria, Lactobacillus fermentum RC4 were grown in broth containing NaNO2 at 0, 100, 300, or 500 mg/L, and 8-plex iTRAQ proteomics and bioinformatics analysis were employed to explore protein expression patterns during nitrite degradation. Real-time PCR was used to confirm mRNA expression levels of selected genes. In the 100, 300, and 500 mg/L sodium nitrite groups, 31, 87, and 190 differentially expressed proteins (DEPs) were identified, of which 24, 57, and 109 were up-regulated and 7, 30, and 81 were down-regulated. Gene ontology (GO) and Kyoto Encyclopaedia of genes and genomes (KEGG) analyses of DEPs indicated that adhE and lpdA involved in carbohydrate metabolism, cysK linked to amino acid metabolism, nirB related to nitrogen metabolism, fabI and accD associated with lipid metabolism, and gsk involved in nucleotide metabolism were dramatically differentially expressed. Nitrogen metabolism is essential for maintaining nitrogen balance, and the above genes appear to be involved in L. fermentum RC4 growth and development during nitrite reduction. These novel proteomics results provide new insight into the potential mechanism nitrite degradation by L. fermentum. BIOLOGICAL SIGNIFICANCE: Nitrite helps meat products retain colour and prevents decay, but excessive intake can be carcinogenic. The probiotic L. fermentum RC4 can degrade nitrite but the mechanism is poorly understood. Herein, we performed quantitative proteomic profiling of L. fermentum RC4 using the iTRAQ approach, and identified various mechanisms potentially involved in nitrite degradation, including carbohydrate, amino acid, lipid, nucleotide, and nitrogen metabolic pathways. This is the first iTRAQ proteomic analysis of nitrite degradation by L. fermentum RC4, and the results provide novel insight.