The predicted acetoin dehydrogenase pathway represses sporulation of .

UNLABELLED

is a major gastrointestinal pathogen that is transmitted as a dormant spore. As an intestinal pathogen, must contend with variable environmental conditions, including fluctuations in pH and nutrient availability. Nutrition and pH both influence growth and spore formation, but how pH and nutrition jointly influence sporulation are not known. In this study, we investigated the dual impact of pH and pH-dependent metabolism on sporulation. Specifically, we examined the impacts of pH and the metabolite acetoin on growth and sporulation. We found that expression of the predicted acetoin dehydrogenase operon, , was pH-dependent and regulated by acetoin. Regulation of the locus is distinct from other characterized systems and appears to involve a co-transcribed DeoR-family regulator rather than the sigma -dependent activator. In addition, an null mutant produced significantly more spores and initiated sporulation earlier than the parent strain. However, unlike other Firmicutes, growth and culture density of was not increased by acetoin availability or disruption of the pathway. Together, these results indicate that acetoin, pH, and the pathway play important roles in nutritional repression of sporulation in , but acetoin metabolism does not support cell growth as a stationary phase energy source.

IMPORTANCE

or , is an anaerobic bacterium that lives within the gut of many mammals and causes infectious diarrhea. is able to survive outside of the gut and transmit to new hosts by forming dormant spores. It is known that the pH of the intestine and the nutrients available both affect the growth and sporulation of but the specific conditions that result in sporulation in the host are not clear. In this study, we investigated how pH and the metabolite acetoin affect the ability of to grow, proliferate, and form spores. We found that a mutant lacking the predicted acetoin metabolism pathway form more spores, but their growth is not impacted. These results show that uses acetoin differently than many other species and that acetoin has an important role as an environmental metabolite that influences spore formation.