Abstract
Previous studies showed that γ-Aminobutyric Acid (GABA) can protect some GABA-producing bacteria against acid stress through glutamate decarboxylation. However, the acid stress mechanism is a comprehensive network related to numerous genes and proteins. Other than the Glutamate Decarboxylase (GAD)/GABA antiporter system, limited information is available about the physiological modifications that occur in Lactobacillus brevis during GABA production under acidic conditions. Therefore, this study aims to investigate the physiological modifications that occur in a GABA-producing L. brevis NCL912 during GABA production under acidic conditions. The differential protein expression of L. brevis NCL912 under different culture conditions was determined by using proteome analysis. Eleven of the protein spots were identified by mass spectrometry. Among the 11 proteins, 10 were upregulated, whereas one was downregulated. The function of downregulated protein was unknown. The upregulated proteins were involved in stress response, protein synthesis, quorum sensing, glycolysis and membrane lipid synthesis. Stress response, protein synthesis, glycolysis-related proteins are general acid stress proteins, while LuxS-dependent quorum sensing system and membrane lipid synthesis-related proteins might be induced by sodium L-glutamate during GABA production under acid stress. In conclusion, sodium L-glutamate might trigger other acid-tolerance responses, except the GAD/GABA system in L. brevis NCL912 during GABA production under acidic conditions.
Highlights
Lactobacillus is generally regarded as safe to humans
Except for the Glutamate Decarboxylase (GAD)/GABA antiporter system, little is known about the physiological modifications that occur in L. brevis NCL912during GABA production under acid conditions
System and membrane lipid synthesis-related proteins were up-regulated. All these suggested that stress response, protein synthesis, glycolysis-related proteins are general acid stress proteins, while LuxS-dependent Quorum Sensing (QS) system and membrane lipid synthesis-related proteins might be induced by L-MSG during GABA production under acid stress
Summary
Lactobacillus is generally regarded as safe to humans. These bacteria serve an important function in the food industry. Researchers have exerted considerable effort to select more new Lactobacillus strains with functional properties for fermented products because of the positive effects of lactobacillus on human health. Only a limited number of Lactobacillus can be used in commercial food products or probiotics because Lactobacillus performance under optimal laboratory conditions might be difficult to achieve under typical processing conditions. Acid tolerance is one of the main characteristics that Lactobacillus should possess under stress conditions. Mechanisms contributing to the capacity of Lactobacillus to tolerate acidic pH are essential to the production and functionality of a probiotic culture (Azcarate-Peril et al, 2004)
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