POPULATION-DYNAMICS IN THE COCULTURE OF SHIGELLA-FLEXNERI 1B ORIGINALSTRAIN AND ITS ANTIGENIC 3B MUTANT CARRYING A PROPHAGE

The antigenic mutant Shigella flexneri 3b showed selective prevalence when subcultured with the original strain 1b. Mathematical analysis of such co-cultures showed that the dynamics of bacterial growth may be described by equations of the Lotka-Volterra type. The analysis of ser ial cultivations suggests that parameters of the equations may be real izations of random variables characterizing strains and media. The mut ant carries a prophage lethal for the original strain. Distinctive fea tures of the growth of these strains alone and in co-culture may be su ccessfully explained by the differences in growth parameters, without phage inference. The concurrence model connected only with the existen ce of the phage is not sufficient. A complete description of the dynam ics of the co-culture is obtained by the connection of the assumptions of two models: strains in competition and growth of strains with phag e, given the random character of the parameters.