Mutations of the Corynebacterium glutamicum NCgl1221 Gene, Encoding a Mechanosensitive Channel Homolog, Induce l-Glutamic Acid Production

ABSTRACT

Corynebacterium glutamicum is a biotin auxotroph that secretes l-glutamic acid in response to biotin limitation; this process is employed in industrial l-glutamic acid production. Fatty acid ester surfactants and penicillin also induce l-glutamic acid secretion, even in the presence of biotin. However, the mechanism of l-glutamic acid secretion remains unclear. It was recently reported that disruption of odhA, encoding a subunit of the 2-oxoglutarate dehydrogenase complex, resulted in l-glutamic acid secretion without induction. In this study, we analyzed odhA disruptants and found that those which exhibited constitutive l-glutamic acid secretion carried additional mutations in the NCgl1221 gene, which encodes a mechanosensitive channel homolog. These NCgl1221 gene mutations lead to constitutive l-glutamic acid secretion even in the absence of odhA disruption and also render cells resistant to an l-glutamic acid analog, 4-fluoroglutamic acid. Disruption of the NCgl1221 gene essentially abolishes l-glutamic acid secretion, causing an increase in the intracellular l-glutamic acid pool under biotin-limiting conditions, while amplification of the wild-type NCgl1221 gene increased l-glutamate secretion, although only in response to induction. These results suggest that the NCgl1221 gene encodes an l-glutamic acid exporter. We propose that treatments that induce l-glutamic acid secretion alter membrane tension and trigger a structural transformation of the NCgl1221 protein, enabling it to export l-glutamic acid.