ALTERED EXPRESSION OF SEVERAL GENES IN III(L)MAN-DEFECTIVE MUTANTS OF STREPTOCOCCUS-SALIVARIUS DEMONSTRATED BY 2-DIMENSIONAL GEL-ELECTROPHORESIS OF CYTOPLASMIC PROTEINS

Mannose, glucose and fructose are transported in Streptococcus salivarius by a phosphoenolpyruvate: mannose phosphotransferase system (PTS) which consists of a membrane-bound Enzyme II (EII) and two forms of III(Man) having molecular weights of 38,900 (III(H)Man) and 35,200 (III(L)Man), respectively. We have previously reported the isolation of spontaneous mutants lacking III(L)Man and showed that they exhibit higher galactosidase activity than the parental strain after growth on glucose, and that some of them constitutively express a fructose PTS which is induced by fructose in the parental strain. In an attempt to determine whether the expression of other genes is affected by the mutation and what the physiological link is between them, we examined three S. salivarius III(L)Man-defective mutants (strains A37, B31 and G29) and the parental strain using two-dimensional gel electrophoresis after growth of the cells on a variety of sugars. After growth on glucose, five new proteins were detected in the cytoplasm of the three mutants. Two of these proteins were induced in the parental strain by galactose or oligosaccharides containing galactose, and one was specifically induced by melibiose. The other two proteins were not detected in the parental strain under any of the growth conditions tested. Two other proteins were only detected in glucose-grown cells of mutant A37, and a protein associated with the metabolism of fructose was constitutively expressed in mutants B31 and G29. Moreover, we have found that under identical growth conditions the amounts of several other proteins which were detected in the parental strain were either increased or decreased in the mutants. Globally, our results have indicated that (1) the expression of several genes was affected in the spontaneous III(L)Man-defective mutants; (2) some of the proteins abnormally produced in the mutants were specifically induced in the parental strain by sugars; (3) the phenotypic modifications observed in the mutants were of two types: most were observed solely after growth of the cells on glucose whereas the others were glucose-independent; and (4) the mutants shared common phenotypic traits, but also exhibited idiosyncratic characteristics.