An evaluation of allozyme amino acid substitutions for the study of molecular relationships in Providencia strains

Through analysis of molecular relationships in terms of amino acid substitutions, intra- and interspecies differentiations in Providencia alcalifaciens, P. stuartii and P. rustigianii were evaluated among the electrophoretic variants of three enzymes, L-malate dehydrogenase, acid phosphatase and esterase-βa, chosen for their distinct pattern of polymorphism. For each enzyme, molecular relatedness among variants defined by two-dimensional electrophoretic profiles was examined through protein titration curves. P. stuartii strains appeared identical to each other and P. rustigianii strains were closely related, whereas the division of P. alcalifaciens strains into previously described zymotypes A₁ and A₂ was refined in molecular terms. A gradient of molecular interrelatedness between the species was observed for the three enzyme loci: with L-malate dehydrogenase, the three species appeared very closely related; with acid phosphatase, P. stuartii and P. alcalifaciens were more closely related to each other than to P. rustigianii; with esterase-βa, P. alcalifaciens and P. stuartii appeared partially related, whereas no such relatedness was observed between these two species and P. rustigianii.