Whole genome sequencing of Lactobacillus plantarum DMDL 9010 and its effect on growth phenotype under nitrite stress

The nitrite that normally exists in fermented foods is a threat to public health. Nitrite degradation by lactic acid bacteria (LAB) has the advantages of safety and low cost. This study investigated the effect of Lactobacillus plantarum DMDL 9010 (LP9010) on growth phenotype under nitrite stress from the perspective of whole genome sequencing. The results showed that LP9010 has certain tolerance to nitrite. However, high nitrite concentration (5-12.5 mmol/L) inhibited the growth and acid production. Nitrite could not only affect the morphology of LP9010 cells with longer phenotype, shrink and dent on the surface (even crack), but also decreased cell surface hydrophobicity. Correspondingly, 19 genes encoding stress proteins have been found in the genome. In addition, genes related to osmotic regulation proteins and peptidoglycans synthesis were found in the genome of LP9010, which may affect the cell wall structure under nitrite stress. Low pH lactic acid could degrade nitrite, whereas nitrite was hardly degraded when pH > 4. In addition, we found the putative nitrite reductase gene in LP9010, the nitrite ion bound to the Cd1NiR (pgl) active site by forming two hydrogen bonds with the residues PRO87 and PRO88. This study could provide theoretical reference to reduce nitrite in food products.