Second messenger signaling in Clostridioides difficile

RelQ-mediated alarmone signaling regulates growth, sporulation, and stress-induced biofilm formation in Clostridioides difficile

The bacterial stringent response (SR) is a conserved transcriptional reprogramming pathway mediated by the nucleotide signaling alarmones, (pp)pGpp. The SR has been implicated in antibiotic survival in Clostridioides difficile, a biofilm- and spore-forming pathogen that causes resilient, highly recurrent C. difficile infections. The role of the SR in other processes and the effectors by which it regulates C. difficile physiology are unknown. C. difficile RelQ is a clostridial alarmone synthetase. Deletion of relQ dysregulates C. difficile growth in unstressed conditions, affects susceptibility to antibiotic and oxidative stressors, and drastically reduces biofilm formation. While wild-type C. difficile displays increased biofilm formation in the presence of sub-lethal stress, the ΔrelQ strain cannot upregulate biofilm production in response to stress. Deletion of relQ slows spore accumulation in planktonic cultures but accelerates it in biofilms. This work establishes biofilm formation and sporulation as alarmone-mediated processes in C. difficile and reveals the importance of RelQ in stress-induced biofilm regulation.

Expanding our grasp of two-component signaling in Clostridioides difficile

The intestinal pathogen Clostridioides difficile encodes roughly 50 TCS, but very few have been characterized in terms of their activating signals or their regulatory roles. A. G. Pannullo, B. R. Zbylicki, and C. D. Ellermeier (J Bacteriol 205:e00164-23, 2023, https://doi.org/10.1128/jb.00164-23) have identified both for the novel C. difficile TCD DraRS. DraRS responds to antibiotics that target lipid-II molecules in the bacterial cell envelope, and regulates the production of a novel glycolipid necessary for bacitracin and daptomycin resistance in C. difficile.

Type IV pili are involved in phenotypes associated with Clostridioides difficile pathogenesis

Clostridioides difficile is a Gram-positive, spore-forming, rod-shaped, obligate anaerobe that is the leading cause of antibiotic-associated diarrhea. Type IV pili (T4P) are elongated appendages on the surface of C. difficile that are polymerized from many pilin proteins. T4P play an important role in C. difficile adherence and particularly in its persistence in the host intestine. Recent studies have shown that T4P promote C. difficile aggregation, surface motility, and biofilm formation, which may enhance its pathogenicity. Additionally, the second messenger cyclic diguanylate increases pilA1 transcript abundance, indirectly promoting T4P-mediated aggregation, surface motility, and biofilm formation of C. difficile. This review summarizes recent advances in C. difficile T4P research and the physiological activities of T4P in the context of C. difficile pathogenesis.

Rounding out cyclic dinucleotide signaling in Clostridioides difficile: A role and a mechanism for c-di-AMP

The second messenger c-di-AMP contributes to various homeostatic and stress responses in bacteria. In this issue of Science Signaling, Oberkampf et al. have identified it as a mediator of osmotic stress and bile salt resistance in the opportunistic pathogen Clostridioides difficile, with additional roles in cell wall homeostasis and biofilm formation.