Nitrite reductases of lactic acid bacteria: Regulation of enzyme synthesis and activity, and different applications

Nitrite (NIT) can be degraded by lactic acid bacteria (LAB) via three pathways, including reduction by nitrite reductase (NiR), acid, and certain metabolites, where enzymatic degradation is the dominant form. This review discusses the classification, structure, and related genes of NiR, as well as the process of NIT degradation, the influencing factors, and the main applications in food and the environment. NiRs are classified into four categories, namely, copper-type reductases (CuNiRs), cytochrome cd1-type reductases (cd1NiRs), iron redox-dependent reductases (FdNiRs), and polyhemoglobin c reductases (ccNiRs). NIT via the nirK/nirS genes encoding CuNiRs/cd1NiRs reduces residual NIT from natural and anthropogenic activities to nitric oxide (NO). CuNiRs and cd1NiRs can accept extracellular NO3− and bind to the enzyme-activated intracellular receptor proteins for further degradation to NO2− are affected by various internal and external factors, such as structural sites and pH. NiR generated from LAB has extensive applications mainly in the food industry and environment, which will be beneficial to promote low-nitrification life and maintain the ecological environment, having a good application prospect.