Characterization of myo -Inositol Utilization by Corynebacterium glutamicum : the Stimulon, Identification of Transporters, and Influence on l -Lysine Formation

Abstract

Although numerous bacteria possess genes annotated iol in their genomes, there have been very few studies on the possibly associated myo -inositol metabolism and its significance for the cell. We found that Corynebacterium glutamicum utilizes myo -inositol as a carbon and energy source, enabling proliferation with a high maximum rate of 0.35 h ⁻¹ . Whole-genome DNA microarray analysis revealed that 31 genes respond to myo -inositol utilization, with 21 of them being localized in two clusters of >14 kb. A set of genomic mutations and functional studies yielded the result that some genes in the two clusters are redundant, and only cluster I is necessary for catabolizing the polyol. There are three genes which encode carriers belonging to the major facilitator superfamily and which exhibit a >12-fold increased mRNA level on myo -inositol. As revealed by mutant characterizations, one carrier is not involved in myo -inositol uptake whereas the other two are active and can completely replace each other with apparent K _m s for myo -inositol as a substrate of 0.20 mM and 0.45 mM, respectively. Interestingly, upon utilization of myo -inositol, the l -lysine yield is 0.10 mol/mol, as opposed to 0.30 mol/mol, with glucose as the substrate. This is probably not only due to myo -inositol metabolism alone since a mixture of 187 mM glucose and 17 mM myo -inositol, where the polyol only contributes 8% of the total carbon, reduced the l -lysine yield by 29%. Moreover, genome comparisons with other bacteria highlight the core genes required for growth on myo -inositol, whose metabolism is still weakly defined.