A regulatory protein that represses sporulation inClostridioides difficile

Abstract

Bacteria that reside in the gastrointestinal tract of healthy humans are essential for our health, sustenance and well-being. About 50 to 60% of those bacteria have the ability to produce resilient spores, important for the life cycle in the gut and for host-to-host transmission. A genomic signature for sporulation in the human intestine was recently described, which spans both commensals and pathogens such as Clostridioides difficile, and contains several genes of unknown function. We report on the characterization of a signature gene, csiA, which, as we show, is involved in the control of sporulation initiation in C. difficile. Spo0A is the main regulatory protein controlling entry into sporulation and we show that an in-frame deletion of csiA results in increased sporulation, and increased expression of spo0A per cell. Spo0A also drives transcription of the spoIIA and spoIIG operons, coding for the first forespore-(σF) and mother cell-specific (σE) RNA polymerase sigma factors. Strikingly, deletion of csiA increases expression of the spoIIG operon, but not that of the spoIIA operon. Increased expression of spoIIG results in increased production and proteolytic activation of pro-σE, suggesting that normally, the levels of active σE are limiting for sporulation. While other regulatory proteins affect both sporulation and several processes during the transition phase of growth, including toxin production or motility, deletion of the csiA gene does not alter the expression of the genes coding for the TcdA and TcdB cytotoxins or the genes involved in motility. Thus, our results establish that CsiA acts to modulate sporulation by reducing expression of the spo0A gene.

Host adaptation in gut Firmicutes is associated with sporulation loss and altered colonisation patterns

“…Using this collection, we determined their sporulation capacity, by establishing the presence of 66 sporulation-predictive genes identified using a previously developed machine learning model based on analysis of nearly 700,000 genes and 234 genomes from bacteria with an ethanol sensitive or ethanol resistant phenotype 23 . Genes in this sporulation signature include characterised sporulation-associated genes, characterised genes not previously associated with sporulation and uncharacterised genes that have subsequently been demonstrated to be sporulation-associated 30 .…”