AUTHOR=Zhu Lingfeng , Mack Christina , Wirtz Astrid , Kranz Angela , Polen Tino , Baumgart Meike , Bott Michael 

TITLE=Regulation of γ-Aminobutyrate (GABA) Utilization in Corynebacterium glutamicum by the PucR-Type Transcriptional Regulator GabR and by Alternative Nitrogen and Carbon Sources

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.544045

DOI=10.3389/fmicb.2020.544045

ISSN=1664-302X

ABSTRACT=<p>γ-Aminobutyric acid (GABA) is a non-proteinogenic amino acid mainly formed by decarboxylation of <sc>L</sc>-glutamate and is widespread in nature from microorganisms to plants and animals. In this study, we analyzed the regulation of GABA utilization by the Gram-positive soil bacterium <italic>Corynebacterium glutamicum</italic>, which serves as model organism of the phylum <italic>Actinobacteria.</italic> We show that GABA usage is subject to both specific and global regulatory mechanisms. Transcriptomics revealed that the <italic>gabTDP</italic> genes encoding GABA transaminase, succinate semialdehyde dehydrogenase, and GABA permease, respectively, were highly induced in GABA-grown cells compared to glucose-grown cells. Expression of the <italic>gabTDP</italic> genes was dependent on GABA and the PucR-type transcriptional regulator GabR, which is encoded divergently to <italic>gabT</italic>. A Δ<italic>gabR</italic> mutant failed to grow with GABA, but not with glucose. Growth of the mutant on GABA was restored by plasmid-based expression of <italic>gabR</italic> or of <italic>gabTDP</italic>, indicating that no further genes are specifically required for GABA utilization. Purified GabR (calculated mass 55.75 kDa) formed an octamer with an apparent mass of 420 kDa and bound to two inverted repeats in the <italic>gabR</italic>-<italic>gabT</italic> intergenic region. Glucose, gluconate, and <italic>myo</italic>-inositol caused reduced expression of <italic>gabTDP</italic>, presumably via the cAMP-dependent global regulator GlxR, for which a binding site is present downstream of the <italic>gabT</italic> transcriptional start site. <italic>C. glutamicum</italic> was able to grow with GABA as sole carbon and nitrogen source. Ammonium and, to a lesser extent, urea inhibited growth on GABA, whereas <sc>L</sc>-glutamine stimulated it. Possible mechanisms for these effects are discussed.</p>