Australia: The Land Where Time Began

A biography of the Australian continent 

Slime Mould Dictyostelium discoideum - A Single Mutation in the gacA Gene Converted a Bacterial Symbiont to Food

Benefit to all partners is required for multipartite mutualistic associations to remain stable. In this paper Stallforth et al. show how a symbiotic bacterium has been changed from an inedible producer of secondary metabolite that is beneficial to the host into a food source for the host by a single mutational step. The host of the bacterium is a farmer clone of Dictyostelium discoideum, a social amoeba, which carries and disperses bacteria during its spore stage. Of 2 strains of Pseudomonas fluorescens only 1 is used as a source of food. The nonfood source strain produces small diffusible molecules, a known antifungal agent, pyrrolnitrin, and a chromene that has the potential of enhancing the spore production of the farmer clone and depresses sore production in a non-farmer clone. A derived point mutation in the food strain that generates a premature stop codon in a global activator (gacA), which encodes the response regulator of a 2-component regulatory system, has been identified by genome sequence and phylogenetic analyse. The secondary metabolite profile of the nonfood bacterial strain has been altered by the generation of a knockout mutant of this regulatory gene to match that of the food strain, and also converted it to a food source independently. These results suggest that a single mutation of an indelible ancestral strain that served a protective role converted it to a “domesticated” food source,

Sources & Further reading

1. Stallforth, P., D. A. Brock, A. M. Cantley, X. Tian, D. C. Queller, J. E. Strassmann and J. Clardy (2013). "A bacterial symbiont is converted from an inedible producer of beneficial molecules into food by a single mutation in the gacA gene." Proceedings of the National Academy of Sciences.