Regulation Mechanism of Nitrite Degradation in Lactobacillus plantarum WU14 Mediated by Fnr

Fumarate and nitrate reduction regulatory protein (Fnr), as a global transcriptional regulator, could directly or indirectly regulate many genes in different metabolic pathways at the top of the bacterial transcription regulation network. The present study aimed to explore the regulatory mechanism of Fnr-mediated nitrite degradation in Lactobacillus plantarum WU14 through gene transcription and expression analysis of oxygen sensing and nir operon expression regulation by Fnr, and the interaction and the mechanism of transcriptional regulation between Fnr and GlnR under nitrite stress. After the purification of Fnr and GlnR by GST tags, they were successfully expressed in Escherichia coli by constructing an expression vector. The electrophoresis mobility shift assay and qRT-PCR results indicated that Fnr could specifically bind to the PglnR and Pnir promoters and regulate the expression of nitrite reductase (Nir) and GlnR. After 6-12 h of culture, the expression of fnr and nir under anaerobic condition (A) were higher than that under aerobic condition (O), and the expression of these two genes increased with the addition of NaNO ₂ during aerobic culture. Overall, the present study results indicated that Fnr could not only directly participate in the expression of Nir and GlnR but also indirectly regulate the expression of Nir through GlnR regulation.