Microbial Synergy via an Ethanol-Triggered Pathway

Abstract

We have discovered a microbial interaction between yeast, bacteria, and nematodes. Upon coculturing, Saccharomyces cerevisiae stimulated the growth of several species of Acinetobacter, including, A. baumannii, A. haemolyticus, A. johnsonii, and A. radioresistens, as well as several natural isolates of Acinetobacter. This enhanced growth was due to a diffusible factor that was shown to be ethanol by chemical assays and evaluation of strains lacking ADH1, ADH3, and ADH5, as all three genes are involved in ethanol production by yeast. This effect is specific to ethanol: methanol, butanol, and dimethyl sulfoxide were unable to stimulate growth to any appreciable level. Low doses of ethanol not only stimulated growth to a higher cell density but also served as a signaling molecule: in the presence of ethanol, Acinetobacter species were able to withstand the toxic effects of salt, indicating that ethanol alters cell physiology. Furthermore, ethanol-fed A. baumannii displayed increased pathogenicity when confronted with a predator, Caenorhabditis elegans. Our results are consistent with the concept that ethanol can serve as a signaling molecule which can affect bacterial physiology and survival.

We thank John McCusker for the pathogenic yeast strains and Andre Lachance for the natural yeast isolates. We also thank Nick Ornston, Arnold Barton, Thomas Burr, and Stefan Pukatzki for bacterial strains. The work involving C. elegans could not have been performed without the assistance of Frank Slack and his lab, in particular, Monica Vella and Stephen Johnson. We also thank William Firshein, Anthony Infante, Dan Nowakowski, Dan Gelperin, Antonio Casamoyer, and Anthony Borneman for their critical reviews of the manuscript. M.G.S. especially thanks Dave Young for strains, suggestions, and invaluable support.