Plasmodial slime molds and the evolution of microbial husbandry

Detailed analyses into the life cycle of the soil-dwelling microbe Dictyostelium discoideum led to the conclusion that this "social amoeba" practices some form of "non-monoculture farming" via the transfer of bacteria to novel environments. Herein, we show that in myxomycetes (plasmodial slime molds or myxogastrids) a similar "farming symbiosis" has evolved. Based on laboratory studies of two representative species in the genera Fuligo and Didymium, the sexual life cycle of these enigmatic microbes that feed on bacteria was reconstructed, with reference to plasmo- and karyogamy. We document that the spores carry and transfer bacteria and hence may inoculate new habitats. The significance of this finding with respect to Ernst Haeckel's work on myxomycetes and his concept of ecology are addressed.