Influence of nitrogen sources on the tolerance of Lacticaseibacillus rhamnosus to heat stress and oxidative stress

Abstract

It has been found that 32 genes related to nitrogen source metabolism in Lacticaseibacillus rhamnosus are downregulated under both heat stress and oxidative stress. In this study, the influence of different nitrogen sources within the growth medium on the tolerance of L. rhamnosus to heat stress and oxidative stress was investigated. Tryptone-free MRS was found to enhance the tolerance of L. rhamnosus hsryfm 1301 to heat stress and oxidative stress during the whole growth period, and this result was universal for all L. rhamnosus species analyzed. The strongest strengthening effect occurred when the OD600 value reached 2.0, at which the survival rates under heat stress and oxidative stress increased 130 fold and 40 fold, respectively. After supplementing phenylalanine, isoleucine, glutamate, valine, histidine, or tryptophan into the tryptone-free MRS, the tolerance of L. rhamnosus to heat stress and oxidative stress exhibited a sharp drop. The spray drying survival rate of L. rhamnosus hsryfm 1301 cultured in the tryptone-free MRS rose to 75% (from 30%), and the spray dried powder also performed better in the experimentally simulated gastrointestinal digestion. These results showed that decreasing the intake of amino acids is an important mechanism for L. rhamnosus to tolerate heat stress and oxidative stress. When L. rhamnosus is cultured for spray drying, the concentration of the nitrogen source's components should be an important consideration.

Transcriptome-phenotype matching analysis of how nitrogen sources influence Lacticaseibacillus rhamnosus tolerance to heat stress and oxidative stress

“…The H-OST of L. rhamnosus hsryfm 1301 cultured in NP-MRS broth was significantly stronger than that from MRS broth or NP-MRS broth supplemented with phenylalanine, isoleucine, glutamate, valine, histidine, or tryptophan. The spray drying survival rate of L. rhamnosus hsryfm 1301 cultured in NP-MRS broth rose to 75% (from 30% in MRS broth) [ 16 ]. Therefore, these results helped reveal the underlying mechanisms of stress responses.…”

“…MRS, NP-MRS (tryptone-free MRS) and Phe-MRS (addition of Phe to NP-MRS with a final concentration of 0.8 g L −1 ) broths were prepared according to our previous study [ 16 ]. Sugar supplement media were prepared with the addition of mannose, fructose, galactose, or ribose to the glycoprival MRS medium (Table 1 10 g L −1 ) [ 30 ].…”

“…The spray-drying survival rate of L. rhamnosus hsryfm 1301 cultured in tryptone-free MRS broth rose to 75% (from 30%), and the spray-dried powder also exhibited higher survival in simulated gastrointestinal digestion. After supplementing tryptone-free MRS broth with phenylalanine, isoleucine, glutamate, valine, histidine, or tryptophan, the H-OST of L. rhamnosus hsryfm 1301 exhibited a sharp drop [ 16 ]. Amino acids often played a positive role in stress resistance of LAB [ 9 , 17 ].…”