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

Mannose, glucose and fructose are transported in Streptococcus salivar ius by a phosphoenolpyruvate: mannose phosphotransferase system (PTS) which consists of a membrane-bound Enzyme II (EII) and two forms of II I(Man) having molecular weights of 38,900 (III(H)Man) and 35,200 (III( L)Man), respectively. We have previously reported the isolation of spo ntaneous mutants lacking III(L)Man and showed that they exhibit higher galactosidase activity than the parental strain after growth on gluco se, and that some of them constitutively express a fructose PTS which is induced by fructose in the parental strain. In an attempt to determ ine 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 gr owth of the cells on a variety of sugars. After growth on glucose, fiv e new proteins were detected in the cytoplasm of the three mutants. Tw o of these proteins were induced in the parental strain by galactose o r oligosaccharides containing galactose, and one was specifically indu ced by melibiose. The other two proteins were not detected in the pare ntal strain under any of the growth conditions tested. Two other prote ins were only detected in glucose-grown cells of mutant A37, and a pro tein associated with the metabolism of fructose was constitutively exp ressed in mutants B31 and G29. Moreover, we have found that under iden tical growth conditions the amounts of several other proteins which we re detected in the parental strain were either increased or decreased in the mutants. Globally, our results have indicated that (1) the expr ession of several genes was affected in the spontaneous III(L)Man-defe ctive mutants; (2) some of the proteins abnormally produced in the mut ants were specifically induced in the parental strain by sugars; (3) t he phenotypic modifications observed in the mutants were of two types: most were observed solely after growth of the cells on glucose wherea s the others were glucose-independent; and (4) the mutants shared comm on phenotypic traits, but also exhibited idiosyncratic characteristics .