Production of Gamma-Aminobutyric Acid from Lactic Acid Bacteria: A Systematic Review

Abstract

Gamma-aminobutyric acid (GABA) is widely distributed in nature and considered a potent bioactive compound with numerous and important physiological functions, such as anti-hypertensive and antidepressant activities. There is an ever-growing demand for GABA production in recent years. Lactic acid bacteria (LAB) are one of the most important GABA producers because of their food-grade nature and potential of producing GABA-rich functional foods directly. In this paper, the GABA-producing LAB species, the biosynthesis pathway of GABA by LAB, and the research progress of glutamate decarboxylase (GAD), the key enzyme of GABA biosynthesis, were reviewed. Furthermore, GABA production enhancement strategies are reviewed, from optimization of culture conditions and genetic engineering to physiology-oriented engineering approaches and co-culture methods. The advances in both the molecular mechanisms of GABA biosynthesis and the technologies of synthetic biology and genetic engineering will promote GABA production of LAB to meet people's demand for GABA. The aim of the review is to provide an insight of microbial engineering for improved production of GABA by LAB in the future.

Keywords: co-culture engineering; gamma-aminobutyric acid; genetic engineering; lactic acid bacteria; physiology.

Figure 1

The biosynthetic pathway of GABA by microbes. GABA-AT, GABA aminotransferase; GadB/GadA, glutamate decarboxylase; GadC, glutamate: γ-aminobutyrate antiporter; GDH, l-glutamate dehydrogenase; GltB, glutamate synthase; Icd, isocitrate dehydrogenase; MDH, malate dehydrogenase; ODHC, 2-oxoglutarate dehydrogenase complex; PC, pyruvate carboxylase; PEP, phosphoenolpyruvate; PEPC, phosphoenolpyruvate carboxylase; SSADH, succinate semialdehyde dehydrogenase; TCA cycle, tricarboxylic acid cycle. The expression of enzymes in green font will increase GABA production, and the expression of enzymes in red font will decrease GABA production.

Figure 2

Genetic organization of the glutamate decarboxylase gene clusters among some lactic acid bacteria (LAB) strains. The number of amino acids within each encoded protein is shown above the corresponding protein. AAP, amino acid permease; Ace, sugar O-acetyltransferase; ACR, amino acid racemase; Ade, adenine deaminase; Adh, zinc-dependent alcohol dehydrogenase family protein; AFA, AAA family ATPase; Akr, aldo/keto reductase; Alt, PLP-dependent aminotransferase family protein; At, metN2, ABC transporter, ATP-binding protein; ATB, ABC transporter ATP-binding protein; ATL, aspartate—tRNA ligase; ATP, ABC transporter permease; Bca, branched-chain amino acid aminotransferase; CAL, carboxylate—amine ligase; CFD, C69 family dipeptidase; CrcB, fluoride efflux transporter; Ctp, cobalt ABC transporter, ATP-binding protein; CTR, Crp/Fnr family transcriptional regulator; DMG, DNA-3-methyladenine glycosylase; DUF, DUF1722 domain-containing protein; DUF1310, DUF1310 family protein; DUF1906, DUF1906 domain-containing protein; DUF4432, DUF4432 family protein; EAL, EAL domain-containing protein; EP, extracellular protein; FCA, formate C-acetyltransferase; FCoAT, formyl-CoA transferase; FtsX, FtsX-like permease family protein; GadB/GadA, glutamate decarboxylase; GadC/GadC1/GadC2, glutamate:gamma-aminobutyrate antiporter; GadR, transcriptional regulator; Gcl, glutamate-cysteine ligase; Gls, glutaminase; GltB, glutamate synthase large subunit; GltC, glutamate synthase subunit beta; GltX, glutamate-tRNA ligase; GuaD, guanine deaminase; Hig, HigA family addiction module antidote protein; Hp, hypothetical protein; HsdS, restriction endonuclease subunit S; HTHP, helix-turn-helix domain-containing protein; LacI, LacI family transcriptional regulator; LarB, nickel pincer cofactor biosynthesis protein; LarC, nickel pincer cofactor biosynthesis protein; LarE, ATP-dependent sacrificial sulfur transferase; LuxS, S-ribosylhomocysteine lyase; LysA, diaminopimelate decarboxylase; LysMP, LysM peptidoglycan-binding domain-containing protein; LysR, LysR family transcriptional regulator; LytF, gamma-d-glutamate-meso-diaminopimelate muropeptidase; MarR, MarR family transcriptional regulator; ME, ImmA/IrrE family metallo-endopeptidase; MFS, MFS transporter; Mic, mechanosensitive ion channel; Mp, membrane protein; MTT, class I SAM-dependent methyltransferase; MurI, glutamate racemase; Nat, N-acetyltransferase; NDLR, nickel-dependent lactate racemase; NDM, N-6 DNA methylase; NPCT, Na/Pi cotransporter family protein; Nudix, NUDIX domain-containing protein; Odr, oxidoreductase; Pck, phosphoenolpyruvate carboxykinase; Per, NCS2 family permease; Pmsk, plasmid maintenance system killer; Rb, ribokinase; Rc, ribonuclease HII; RE, restriction endonuclease; RFP, recombinase family protein; RibY, ribonuclease Y; Rp, 30S ribosomal protein S4; RplQ, ribosomal protein L17; RpoA, DNA-directed RNA polymerase, alpha subunit; SDR, SDR family oxidoreductase; SP, sulfate permease; Spx, Spx/MgsR family RNA polymerase-binding regulatory protein; SseA, sulfurtransferase; Tdk, thymidine kinase; Tn, transposase; TP, l,d-transpeptidase family protein; TR, transcriptional regulator; TSE, threonine/serine exporter family protein; YcxB, YcxB family protein.

Figure 2

Genetic organization of the glutamate decarboxylase gene clusters among some lactic acid bacteria (LAB) strains. The number of amino acids within each encoded protein is shown above the corresponding protein. AAP, amino acid permease; Ace, sugar O-acetyltransferase; ACR, amino acid racemase; Ade, adenine deaminase; Adh, zinc-dependent alcohol dehydrogenase family protein; AFA, AAA family ATPase; Akr, aldo/keto reductase; Alt, PLP-dependent aminotransferase family protein; At, metN2, ABC transporter, ATP-binding protein; ATB, ABC transporter ATP-binding protein; ATL, aspartate—tRNA ligase; ATP, ABC transporter permease; Bca, branched-chain amino acid aminotransferase; CAL, carboxylate—amine ligase; CFD, C69 family dipeptidase; CrcB, fluoride efflux transporter; Ctp, cobalt ABC transporter, ATP-binding protein; CTR, Crp/Fnr family transcriptional regulator; DMG, DNA-3-methyladenine glycosylase; DUF, DUF1722 domain-containing protein; DUF1310, DUF1310 family protein; DUF1906, DUF1906 domain-containing protein; DUF4432, DUF4432 family protein; EAL, EAL domain-containing protein; EP, extracellular protein; FCA, formate C-acetyltransferase; FCoAT, formyl-CoA transferase; FtsX, FtsX-like permease family protein; GadB/GadA, glutamate decarboxylase; GadC/GadC1/GadC2, glutamate:gamma-aminobutyrate antiporter; GadR, transcriptional regulator; Gcl, glutamate-cysteine ligase; Gls, glutaminase; GltB, glutamate synthase large subunit; GltC, glutamate synthase subunit beta; GltX, glutamate-tRNA ligase; GuaD, guanine deaminase; Hig, HigA family addiction module antidote protein; Hp, hypothetical protein; HsdS, restriction endonuclease subunit S; HTHP, helix-turn-helix domain-containing protein; LacI, LacI family transcriptional regulator; LarB, nickel pincer cofactor biosynthesis protein; LarC, nickel pincer cofactor biosynthesis protein; LarE, ATP-dependent sacrificial sulfur transferase; LuxS, S-ribosylhomocysteine lyase; LysA, diaminopimelate decarboxylase; LysMP, LysM peptidoglycan-binding domain-containing protein; LysR, LysR family transcriptional regulator; LytF, gamma-d-glutamate-meso-diaminopimelate muropeptidase; MarR, MarR family transcriptional regulator; ME, ImmA/IrrE family metallo-endopeptidase; MFS, MFS transporter; Mic, mechanosensitive ion channel; Mp, membrane protein; MTT, class I SAM-dependent methyltransferase; MurI, glutamate racemase; Nat, N-acetyltransferase; NDLR, nickel-dependent lactate racemase; NDM, N-6 DNA methylase; NPCT, Na/Pi cotransporter family protein; Nudix, NUDIX domain-containing protein; Odr, oxidoreductase; Pck, phosphoenolpyruvate carboxykinase; Per, NCS2 family permease; Pmsk, plasmid maintenance system killer; Rb, ribokinase; Rc, ribonuclease HII; RE, restriction endonuclease; RFP, recombinase family protein; RibY, ribonuclease Y; Rp, 30S ribosomal protein S4; RplQ, ribosomal protein L17; RpoA, DNA-directed RNA polymerase, alpha subunit; SDR, SDR family oxidoreductase; SP, sulfate permease; Spx, Spx/MgsR family RNA polymerase-binding regulatory protein; SseA, sulfurtransferase; Tdk, thymidine kinase; Tn, transposase; TP, l,d-transpeptidase family protein; TR, transcriptional regulator; TSE, threonine/serine exporter family protein; YcxB, YcxB family protein.

Figure 3

Phylogenetic tree (maximum-likelihood method) based on amino acid sequences of GAD from LAB. Figure was generated from MEGA (version X 10.1) after ClustalW alignment of GADs. The GenBank accession number of GAD is indicated in the braces.