A bacterial symbiont is converted from an inedible producer of beneficial molecules into food by a single mutation in the gacA gene

Authors

Pierre Stallforth, Harvard University
Debra A. Brock, Washington University in St Louis
Alexandra M. Cantley, Harvard University
Xiangjun Tian, Washington University in St Louis
David C. Queller, Washington University in St LouisFollow
Joan E. Strassmann, Washington University in St LouisFollow
Jon Clardy, Harvard University

Author's Department

Biology

Document Type

Article

Publication Date

2013

Abstract

Stable multipartite mutualistic associations require that all partners benefit. We show that a single mutational step is sufficient to turn a symbiotic bacterium from an inedible but host-beneficial secondary metabolite producer into a host food source. The bacteria's host is a "farmer" clone of the social amoeba Dictyostelium discoideum that carries and disperses bacteria during its spore stage. Associated with the farmer are two strains of Pseudomonas fluorescens, only one of which serves as a food source. The other strain produces diffusible small molecules: pyrrolnitrin, a known antifungal agent, and a chromene that potently enhances the farmer's spore production and depresses a nonfarmer's spore production. Genome sequence and phylogenetic analyses identify a derived point mutation in the food strain that generates a premature stop codon in a global activator (gacA), encoding the response regulator of a two-component regulatory system. Generation of a knockout mutant of this regulatory gene in the nonfood bacterial strain altered its secondary metabolite profile to match that of the food strain, and also, independently, converted it into a food source. These results suggest that a single mutation in an inedible ancestral strain that served a protective role converted it to a "domesticated" food source.

Comments

Copyright 2013 by the authors. Open access article published in PNAS September 3, 2013 vol. 110 no. 36 14528-14533. doi: 10.1073/pnas.1308199110

Recommended Citation

Stallforth, Pierre; Brock, Debra A.; Cantley, Alexandra M.; Tian, Xiangjun; Queller, David C.; Strassmann, Joan E.; and Clardy, Jon, "A bacterial symbiont is converted from an inedible producer of beneficial molecules into food by a single mutation in the gacA gene" (2013). Biology Faculty Publications & Presentations. 39.
https://openscholarship.wustl.edu/bio_facpubs/39

Embargo Period

9-5-2013