LAUSR

In this article, the growth, morphological, and genetic responses of Lactobacillus plantarum FQR to nitrite were investigated. The growth and degrading ability of the strain to nitrite was delayed; slight changes were also observed on the cell surface. FQR exposed to 0.120% nitrite exhibited rough surfaces with folds, as shown by scanning electron microscopy. Transmission electron microscopy presented numerous white granules in the FQR incubated without nitrite, compared with FQR exposed to 0.045% and 0.120% nitrite. These granules are common energy storage molecules, which decrease with increasing nitrite concentration. In addition, nitrite reductase (nir) gene and membrane-related genes were activated in varying degrees. A similar trend in relative gene expression indicated that the expression levels of membrane-related genes (with the exception of lp_1403) in FQR increased significantly (p < .05) in the presence of 0.120% nitrite compared with 0.045% nitrite. However, a marked difference was shown for the nir gene in FQR; the nir gene exhibited a relatively low level of expression when exposed to 0.120% nitrite concentration. In summary, the cell morphology and genetic level of L. plantarum FQR were changed in varying degrees after treatment with different nitrite concentrations. Practical Applications Nitrite is an important food additive and nitrite pollution issues of fermented food have become an increasing concern given its potential hazards. L. plantarum has the function of degrading nitrite. However, the detailed mechanisms and pathways involved in the regulation of nitrite in L. plantarum were still unclear. In this article, the growth, morphological, and genetic responses of L. plantarum to nitrite were investigated. It serves as an important reference for future studies of the mechanism of signal transduction in L. plantarum and the mechanism of stress response, and to determine the possible regulating targets. In practice, it can serve as a reference for genetic engineering improvement of L. plantarum used in the fermented food industry reducing nitrite residue.