P117: Analysis of mechanosensitive channels of Corynebacterium glutamicum expressed in Bacillus subtilis

 Corynebacterium glutamicum is used worldwide for the industrial fermentative production of glutamate. However, the mechanism of glutamate secretion remains unclear. It was recently reported that mutation of NCgl1221 resulted in glutamate secretion without induction, and disruption of this gene essentially inhibited glutamate secretion. NCgl1221 encodes a homolog of the small-conductance mechanosensitive channel (MscS). In this study, we analyzed the functions of this protein by using Bacillus subtilis, which expressed the msc genes of C. glutamicum.

 B. subtilis possesses 4 genes that encode mechanosensitive channel homologs. It was reported that cellular survival during osmotic downshock was decreased by disruption of mscL and ykuT. C. glutamicum possesses 2 genes (mscL, mscS) that encode mechanosensitive channel homologs. Therefore, mscL and ykuT double-disruptant strain of B. subtilis was constructed; further, C. glutamicum genes (mscL or mscS) were expressed under the control of xylose promoter.

 Cell survival rate upon osmotic downshock of the mscL and ykuT double-disruptant strain of B. subtilis expressing the mscL or mscS gene of C. glutamicum was increased as compared to that of the double-disruptant of B. subtilis. Moreover, the level of intracellular glutamate, which was taken up under hyperosmotic conditions, of these strains was decreased after osmotic downshock, as compared to that of the double-disruptant of B. subtilis. Further, the mechanosensitive channel activities of these proteins were investigated using the patch-clamp method.

 Our data suggest that the mscL and mscS of C. glutamicum encode mechanosensitive channels, and that these channels are involved in glutamate secretion.