Effect and potential mechanism of nitrite reductase B on nitrite degradation by RC4.

Nitrite has the potential risk of hypoxic poisoning or cancer in pickled food. In our previous study, () RC4 is effective in nitrite degradation by producing nitrite reductase B (NirB). To investigate the detailed mechanism from the genome, response, and regulation of NirB, the whole-genome sequence of RC4 was analyzed, the -EGFP-B with enhanced green fluorescent protein (EGFP) labeled the nitrite reductase large subunit B, and the recombined -NirB with overexpression NirB strain was conducted. The key genes within the dominant metabolism pathways may be involved in stress tolerance to regulate the degrading process. The green fluorescence density of EGFP indicated that NirB activity has a threshold and peaked under 300 mg/L nitrite concentration. NirB overexpressed in RC4 boosted the enzyme activity by 39.6% and the degradation rate by 10.5%, when fermented in 300 mg/L for 40 h, compared to the control group. RNA-seq detected 248 differential genes mainly enriched in carbohydrate, amino acid, and energy metabolism. The A gene for pyruvate metabolism and the N gene for cysteine metabolism were up-regulated. NirB regulates these genes to produce acid and improve stress resistance for RC4 to accelerate nitrite degradation.