The Impact of pH on Clostridioides difficile Sporulation and Physiology.

is a pathogenic bacterium that infects the human colon to cause diarrheal disease. Growth of the bacterium is known to be dependent on certain bile acids, oxygen levels, and nutrient availability in the intestine, but how the environmental pH can influence is mostly unknown. Previous studies indicated that modulates the intestinal pH, and prospective cohort studies have found a strong association between a more alkaline fecal pH and infection. Based on these data, we hypothesized that physiology can be affected by various pH conditions. In this study, we investigated the impact of a range of pH conditions on to assess potential effects on growth, sporulation, motility, and toxin production in the strains 630Δ and R20291. We observed pH-dependent differences in sporulation rate, spore morphology, and viability. Sporulation frequency was lowest under acidic conditions, and differences in cell morphology were apparent at low pH. In alkaline environments, sporulation was greater for strain 630Δ, whereas R20291 produced relatively high levels of spores in a broad range of pH conditions. Rapid changes in pH during exponential growth impacted sporulation similarly among the strains. Furthermore, we observed an increase in motility with increases in pH, and strain-dependent differences in toxin production under acidic conditions. The data demonstrate that pH is an important parameter that affects physiology and may reveal relevant insights into the growth and dissemination of this pathogen. is an anaerobic bacterium that causes gastrointestinal disease. forms dormant spores which can survive harsh environmental conditions, allowing their spread to new hosts. In this study, we determine how intestinally relevant pH conditions impact physiology in the two divergent strains, 630Δ and R20291. Our data demonstrate that low pH conditions reduce growth, sporulation, and motility. However, toxin production and spore morphology were differentially impacted in the two strains at low pH. In addition, we observed that alkaline environments reduce growth, but increase cell motility. When pH was adjusted rapidly during growth, we observed similar impacts on both strains. This study provides new insights into the phenotypic diversity of grown under diverse pH conditions present in the intestinal tract, and demonstrates similarities and differences in the pH responses of different isolates.