Positive selection for resistance to 2‐deoxyglucose gives rise, in Streptococcus salivarius, to seven classes of pleiotropic mutants, including ptsH and ptsl missense mutants

Summary We have used the toxic non‐metabolizabie glucose/ mannose analogue 2‐deoxygiucose to isolate a comprehensive collection of mutants of the phosphoenoipyruvate:sugar phosphotransferase system from Streptococcus salivarius. To increase the range of possible mutations, we isolated spontaneous mutants on different media containing 2‐deoxyglucose and various metabolizable sugars, either lactose, meli‐biose, galactose or fructose. We found that the frequency at which 2‐deoxygiucose‐resistant mutants Were isolated varied according to the growth substrate. The highest frequency was obtained with the combination galactose and 2‐deoxygiucose and was 15‐fold higher than the rate observed with the mixture melibiose and 2‐deoxygiucose, the combination that gave the lowest frequency. By combining results from: (i) Western biol analysis of III Man , a specific component of the phosphoenolpyruvate:mannose phosphotransferase system in S. salivarius ; (ii) rocket immunoelectrophoresis of HPr and EI, the two general energy‐coupling proteins of the phosphotransferase system; and (iii) from gene sequencing, mutants could be assigned to seven classes. Class 1 was composed of strains devoid of III Man L , a low‐molecular‐weight form of III Man L (35200), class 2 was composed of strains exhibiting a reduced level of III Man L , class 3 was composed of strains devoid of both forms of III Man (III Man L as well as III Man H , the high‐molecular‐weight form of III Man (38900)), class 4 was composed of mutants bearing a mutation in ptsH , the gene encoding HPr, class 5 was composed of mutants bearing a mutation in ptsl , the gene encoding EI, class 6 was composed of 2‐deoxygiucose‐resistant strains without any apparent defect in PTS components, and class 7 was composed of strains possessing both forms of III Man but abnormal levels of HPr and/or EI without any mutation in the ptsH and/or the ptsI genes. Preliminary characterization of representative strains of each class is reported.