SELECTION AND FITNESS IN BACTERIOCIN-PRODUCING BACTERIA

Bacteriocins are proteinaceous anticompetitor molecules produced by ba cteria against closely related species. A number of theoretical models have been used to explain experimental data that indicate high polymo rphisms among bacteriocins and a frequency-dependent nature of selecti on for bacteriocin-producing strains. The majority of these experiment al data were, however, obtained from investigations into the colicin g roup of bacteriocins produced by Gram-negative bacteria. The conclusio ns drawn from these models have been extrapolated to other bacteriocin s and allelopathic compounds in general. Examination of more recent ex perimental investigations into the bacteriocins of Gram-positive bacte ria indicate a lower degree of polymorphism and a less frequency-depen dent mode of selection among these strains than among the colicin-prod ucing strains. Here we examine these contradictions in the light of th e assumptions and conclusions of the theoretical models and reported d ata. We show that fitness costs (as indicated by decreased relative ma ximum growth rate) associated with bacteriocin production may be much lower in many cases than is assumed in the present models. A lower fit ness cost associated with bacteriocin production adequately explains t he newer data from Gram-positive bacteria cited here, and indicates th at extrapolation of existing models to all bacteriocins and other alle lopathic compounds is not appropriate.