POSITIVE SELECTION FOR RESISTANCE TO 2-DEOXYGLUCOSE GIVES RISE, IN STREPTOCOCCUS-SALIVARIUS, TO 7 CLASSES OF PLEIOTROPIC MUTANTS, INCLUDINGPTSH AND PTSI MISSENSE MUTANTS

We have used the toxic non-metabolizable glucose/ mannose analogue 2-d eoxyglucose to isolate a comprehensive collection of mutants of the ph osphoenolpyruvate:sugar phosphotransferase system from Streptococcus s alivarius. To increase the range of possible mutations, we isolated sp ontaneous mutants on different media containing P-deoxyglucose and var ious metabolizable sugars, either lactose, melibiose, galactose or fru ctose. We found that the frequency at which 2-deoxyglucose-resistant m utants were isolated varied according to the growth substrate. The hig hest frequency was obtained with the combination galactose and 5-deoxy glucose and was 15-fold higher than the rate observed with the mixture melibiose and P-deoxyglucose, the combination that gave the lowest fr equency. By combining results from: (i) Western blot analysis of IIIMa n, a specific component of the phosphaenolpyruvate:mannose phosphotran sferase system in S. salivarius; (ii) rocket immunoelectrophoresis of HPr and El, the two general energy-coupling proteins of the phosphotra nsferase system; and (iii) from gene sequencing, mutants could be assi gned to seven classes. Class 1 was composed of strains devoid of IIIMa n, a low-molecular-weight form of IIIMan (35 200), class 2 was compose d of strains exhibiting a reduced level of IIILMan, class 3 was compos ed of strains devoid of both forms of IIIMan (IIILMan as well as IIIHM an, the high-molecular-weight form of IIIMan (38900)), class 4 was com posed of mutants bearing a mutation in ptsH, the gene encoding HPr, cl ass 5 was composed of mutants bearing a mutation in ptsi, the gene enc oding El, class 6 was composed of 2-deoxyglucose-resistant strains wit hout any apparent defect in PTS components, and class 7 was composed o f strains possessing both forms of IIIMan but abnormal levels of HPr a nd/or El without any mutation in the ptsH and/or the ptsI genes. Preli minary characterization of representative strains of each class is rep orted.