Novel ribosomal mutations affecting translational accuracy, antibiotic resistance and virulence of Salmonella typhimurium

Many mutations in rpsL cause resistance to, or dependence on, streptomycin and are restrictive (hyperaccurate) in translation. Dependence on streptomy cin and hyperaccuracy can each be reversed phenotypically by mutations in e ither rpsD or rpsE. Such compensatory mutations have been shown to have a r am phenotype (ribosomal ambiguity), increasing the level of translational e rrors. We have shown recently that restrictive rpsL alleles are also associ ated with a loss of virulence in Salmonella typhimurium. To test whether ra m mutants could reverse this loss of virulence, we have isolated a set of r psD alleles in Salmonella typhimurium. We found that the rpsD alleles resto re the virulence of strains carrying restrictive rpsL alleles to a level cl ose to that of the wild type. Unexpectedly, three out of seven mutant rpsD alleles tested have phenotypes typical of restrictive alleles of rpsL, bein g resistant to streptomycin and restrictive (hyperaccurate) in translation. These phenotypes have not been previously associated with the ribosomal pr otein S4. Furthermore, all seven rpsD alleles (four ram and three restricti ve) can phenotypically reverse the hyperaccuracy associated with restrictiv e alleles of rpsL. This is the first demonstration that such compensations do not require that the compensating rpsD allele has a ribosomal ambiguity tram) phenotype.