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

Abstract

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.