B-257. Role of Lgt and Lsp in Maltose Uptake Mediated by Streptococcus mutans Lipoprotein MalE

T. Arimoto, T. Igarashi;
Showa Univ. Sch. of Dent., Tokyo, JAPAN.

Background: Lipoproteins on a bacterial cell surface are thought to be involved with the virulence of bacterial pathogens; however, studies of oral streptococcal lipoproteins have not been reported. To clarify the roles of lipoproteins of a cariogenic pathogen S. mutans, we knocked out the lgt or lsp genes encoding lipoprotein maturation enzymes, identified a lipoprotein (MalE) in the S. mutans lgt-deficient mutant, and examined the function of MalE. Methods: Proteins were analyzed by 2-dimensional gel electrophoresis and identified by Toff-mass analysis. S. mutans mutants lacking the lgt, lsp, malE, ptsI, lgt/ptsI, lsp/ptsI, or malE/ptsI genes were prepared by insertional inactivation of their respective genes. The growth of S. mutans cells was measured in a Trypton based medium (TBM) supplemented with maltose or glucose as a sole carbon source. The maltose uptake was examined with 4-nitirophenyl-α-D-maltoside. Results: Many surface proteins were released in the culture supernatant of the lgt mutant and one of them was identified as a MalE lipoprotein related to the maltose uptake. The growth of the lgt/ptsI, lsp/ptsI and malE/ptsI mutants in TBM with maltose was markedly decreased as compared with that of the lgt, lsp, malE and ptsI mutants. Whereas in the TBM with glucose, a significant difference in growth was not observed among these mutants. The uptake of maltose was reduced in the lgt/ptsI, lsp/ptsI and malE/ptsI mutants. Conclusion: These results suggest that MalE is anchored to the cell membrane by Lgt and is responsible for maltose metabolism as well as the phosphoenolpyruvate-dependent phosphotransferase system (PEP-PTS). In addition, MalE maturation by both Lgt and Lsp are essential for the MalE-mediated uptake of maltose in S. mutans cells.