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Food microbiology

Glutamine, glutamate, and arginine-based acid resistance in Lactobacillus reuteri.


PMID 24929734

Abstract

This study aimed to determine whether glutamine deamidation improves acid resistance of Lactobacillus reuteri, and to assess whether arginine, glutamine, and glutamate-mediated acid resistance are redundant or complementary mechanisms of acid resistance. Three putative glutaminase genes, gls1, gls2, and gls3, were identified in L.xa0reuteri 100-23. All three genes were expressed during growth in mMRS and wheat sourdough. L.xa0reuteri consistently over-expressed gls3 and the glutamate decarboxylase gadB. L.xa0reuteri 100-23ΔgadB over-expressed gls3 and the arginine deiminase gene adi. Analysis of the survival of L.xa0reuteri in acidic conditions revealed that arginine conversion is effective at pH of 3.5 while glutamine or glutamate conversion were effective at pH of 2.5. Arginine conversion increased the pHin but not ΔΨ; glutamate decarboxylation had only a minor effect on the pHin but increased the ΔΨ. This study demonstrates that glutamine deamidation increases the acid resistance of L.xa0reuteri independent of glutamate decarboxylase activity. Arginine and glutamine/glutamate conversions confer resistance to lactate at pH of 3.5 and phosphate at pH of 2.5, respectively. Knowledge of L.xa0reuteri's acid resistance improves the understanding of the adaptation of L.xa0reuteri to intestinal ecosystems, and facilitates the selection of probiotic and starter cultures.