Contribution of phosphoglucosamine mutase to determination of bacterial cell morphology in Streptococcus gordonii

Phosphoglucosamine mutase (GlmM; EC 5.4.2.10) catalyzes the interconversion of glucosamine-6-phosphate to glucosamine-1-phosphate, an essential step in the biosynthetic pathway leading to the formation of the peptidoglycan precursor uridine 5′-diphospho-N-acetylglucosamine. We have recently identified the gene (glmM) encoding the enzyme of Streptococcus gordonii, an early colonizer on the human tooth and an important cause of infective endocarditis, and indicated that the glmM mutation in S. gordonii appears to influence bacterial cell growth, morphology, and sensitivity to penicillins. Moreover, the glmM mutation results in increased sensitivity to polymorphonuclear leukocyte (PMN)-dependent killing. In the present study, we observed similarities in the utilization of sugar between the wild-type strain and the glmM mutant of S. gordonii when cultivated with medium containing 0.2% glucose, fructose, lactose, or sucrose. Morphological analyses clearly indicated that the glmM mutation causes marked elongation of the streptococcal chains, enlargement of bacterial cells, increased distortion of the bacterial cell surface, and defects in cell separation. These results suggest that mutations in glmM appear to influence bacterial cell growth and morphology, independent of the carbon source.