The impact of pH onClostridioides difficilesporulation and physiology

Abstract

ABSTRACTClostridioides difficileis 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 influenceC. difficileis mostly unknown. Previous studies indicated thatC. difficilemodulates the intestinal pH, and prospective cohort studies have found a strong association between a more alkaline fecal pH andC. difficileinfection. Based on these data we hypothesized thatC. difficilephysiology can be affected by various pH conditions. In this study, we investigated the impact of a range of pH conditions onC. difficileto assess potential effects on growth, sporulation, motility and toxin production in the strains 630∆ermand 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,C. difficilesporulation was greater for strain 630∆erm, 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 inC. difficilemotility with increases in pH, and strain-dependent differences in toxin formation under acidic conditions. The data demonstrate that pH is an important parameter that affectsC. difficilephysiology and may reveal relevant insights into the growth and dissemination of this pathogen.IMPORTANCEClostridioides difficileis an anaerobic bacterium that causes gastrointestinal disease.C. difficileforms dormant spores, which can survive harsh environmental conditions, allowing their spread to new hosts. In this study, we determine how intestinally relevant pH conditions impactC. difficilephysiology in the two divergent strains, 630∆erm and R20291. Our data demonstrate that low pH conditions reduceC. difficilegrowth, sporulation, and motility. However, toxin formation and spore morphology are differentially impacted in the strains at low pH. In addition, we observed that alkaline environments reducedC. difficilegrowth, but increased 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 ofC. difficilegrown under the diverse pH conditions present in the intestinal tract, and demonstrates similarities and differences in the pH responses of differentC. difficileisolates.