Isolation, Identification, and Optimization of γ-Aminobutyric Acid (GABA)-Producing Bacillus cereus Strain KBC from a Commercial Soy Sauce moromi in Submerged-Liquid Fermentation

Wan Abd Al Qadr Imad Wan-Mohtar,Safuan Ab Kadir,Zul Ilham,Mohamad Nor Azzimi Sohedein,Mohamad Faizal Ibrahim,Alan Wong Weng Loen,Ooi Poh Suan,Soumaya Sassi

doi:10.3390/pr8060652

Wan Abd Al Qadr Imad Wan-Mohtar, Safuan Ab Kadir + Show 6 more

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https://doi.org/10.3390/pr8060652

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Journal: Processes	Publication Date: May 30, 2020
Citations: 17	License type: CC BY 4.0

Affiliation: University of Malaya, Universiti Putra Malaysia

Abstract

A new high γ-aminobutyric acid (GABA) producing strain of Bacillus cereus was successfully isolated from soy sauce moromi. This B. cereus strain named KBC shared similar morphological characteristics (Gram-positive, rod-shaped) with the reference B. cereus. 16S rRNA sequence of B. cereus KBC was found to be 99% similar with B. cereus strain OPWW1 under phylogenetic tree analysis. B. cereus KBC cultivated in unoptimized conditions using De Man, Rogosa, Sharpe (MRS) broth was capable of producing 523.74 mg L−1 of GABA within five days of the cultivation period. By using response surface methodology (RSM), pH level, monosodium glutamate (MSG) concentration and temperature were optimized for a high concentration of GABA production. The pH level significantly influenced the GABA production by B. cereus KBC with p-value = 0.0023. GABA production by B. cereus KBC under the optimized condition of pH 7, MSG concentration of 5 g L−1 and temperature of 40 °C resulted in GABA production of 3393.02 mg L−1, which is 6.37-fold higher than under unoptimized conditions. Overall, this study has shown that B. cereus KBC isolated from soy sauce moromi is capable of producing a high concentration of GABA together with the optimal fermentation conditions that have been statistically analysed using RSM.

Highlights

Gamma-aminobutyric acid (GABA) is a non-protein amino acid produced by the α-decarboxylation of L-glutamate
The GABA-producing capability of this strain was studied, and the results demonstrated that B. cereus KBC managed to produce 532.74 mg L−1 GABA
The optimisation of GABA production using response surface methodology (RSM) demonstrated that pH significantly influenced the GABA production of B. cereus KBC

Summary

Introduction

Gamma-aminobutyric acid (GABA) is a non-protein amino acid produced by the α-decarboxylation of L-glutamate. The non-protein amino acid is the molecular compound that has the standard structure of an amino acid consisting of N-terminal and C-terminal. Amino acids are classified as non-protein when they are not part of the 22 such. Processes 2020, 8, 652 molecules that are translated into proteins by the standard genetic code [2]. These non-protein amino acids play important roles as metabolites in the organism, function as allelopathic chemicals, nutrient acquisition and in signalling as well as a stress response. Biosynthesis of non-protein amino acid of GABA is catalysed by the glutamate decarboxylase (GAD) enzyme [4]

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Conclusion