Competition and coexistence were examined for two bacterial species, each potentially carrying a fitness-reducing, parasitic plasmid that was vertically transmitted with possible loss through segregation. Here, the fitness reduction of hosts was due to a toxin produced by plasmid-bearing cells and inhibiting plasmid-free cells. These populations were placed in a flow reactor habitat representing an idealized mammal gut. It was numerically shown that parasitic plasmids can mediate coexistence of competing host species, in conditions where plasmid-free hosts could not coexist. Numerical construction of a coexistence example suggests that it arises only for a narrow parameter range. In particular, both rates of segregation and the growth costs of plasmid carriage must be relatively low.
Keywords: Bacteriocin; Coexistence; Colicin; Competition; Flowing habitats; Plasmid.
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