Response Mechanism Of Lactobacillus Plantarum FQR Induced By Nitrite And The Regulation Of Two-component Signal System

Nitrite is an important food additive.However,there is a potential risk of food safety,which has been concerned by people.In this study,L.plantarum FQR has a good ability to degrade nitrite as the research object.The aim of this study was to explore the regulation mechanism of L.plantarum on nitrite and the regulation of the two signal system in order to establish the basis for the regulation of L.plantarum response to nitrite.The main results of this study are as follows:（1）With the increase of NaNO₂concentration,the growth of FQR was inhibited obviously.The high concentration of NaNO₂could inhibit the degradation of L.plantarum,and the activity of nitrite reductase（Ni R）was decreased obviously.NaNO₂caused different degrees of damage to cells,and the greater the concentration of NaNO₂,the higher the permeability of cell membrane.Scanning electron microscopy results showed that high concentration of NaNO₂could cause the surface of FQR cells to fold and sag.In the range of NaNO₂concentration,L.plantarum has a strong ability of automatic regulation,which can resist the damage of NaNO₂to cell membrane.Transmission electron microscopy results showed that the intracellular white particles（the energy storage material in bacteria）decreased in FQR with the increase of NaNO₂concentration,compared with the control group.Under the high concentration of NaNO₂,no white particles were found in the cytoplasm,and the cytoplasm appeared cavitation,which may be caused by the stress response of L.plantarum to the NaNO₂stress environment and the consumption of intracellular energy storage materials.Under different NaNO₂concentrations,membrane-related genes of FQR,Lp＿2037,lp＿0800 and lp＿1403 gene,differentially expressed by 1.04-13.74 times.High concentration of NaNO₂induces the expression of membrane-related genes to enhance the resistance to external environmental persecution.（2）The genes involved in nitrogen metabolism were affected by different concentrations of NaNO₂,and the target genes were expressed in different degrees.Nitrite metabolism pathway of L.plantarum may be global regulated by Gln R.Nitrite was transported to the cell to activate NIR expression by Nir,subsequently was degraded into NH₄⁺by GDH and GS expressed by gdh and gln A respectively,which involved in glutamate metabolism.In addition,the nitrite stimulated expression of L.plantarum involved not only the NIR gene and its downstream genes,but also activated the nitrogen metabolism pathway related genes,such as nar G.（3）The TCSs of L.plantarum 6 strains（WCFS1,P-8,JDM1,16,ZJ316 and ST-III）were predicted by NCBI combined with prokaryotic TCS query system,structure analysis and function It was found that L.plantarum contains 13 typical TCSs,one HK"orphan"and two RR"orphans".And L.plantarum TCSs may be involved in lipid synthesis,hypoxia regulation,quorum sensing,adhesion,biofilm formation,metabolic enzyme synthesis and bacteriocin production.（4）HK4-RR6 and HK6-RR6 may have similar functions as E.coli Nar X-Nar L and Nar Q-Nar P by bioinformatics analysis,which were involved in the regulation of nitrogen metabolism.The results showed that the genes（hk4,rr4,hk6 and rr6）of FQR in different growth periods of different nitrite concentrations exhibited 1.42-9.48 of the expression levels.Hence,HK4-RR4 and HK6-RR6 of L.plantarum TCSs may be involved in the process of nitrite metabolism.In this study,the effects of nitrite on the growth,surface characteristics and morphological structure of L.plantarum were studied.From the molecular level,it can provide important reference for the study of the response mechanism of L.plantarum to nitrite.