Activation of the extracytoplasmic function σ factor σ by lysozyme in Clostridioides difficile.

Clostridioides difficile is naturally resistant to high levels of lysozyme an important component of the innate immune defense system. C. difficile encodes both constitutive as well as inducible lysozyme resistance genes. The inducible lysozyme resistance genes are controlled by an alternative σ factor σ that belongs to the Extracytoplasmic function σ factor family. In the absence of lysozyme, the activity of σ is inhibited by the anti-σ factor RsiV. In the presence of lysozyme RsiV is destroyed via a proteolytic cascade that leads to σ activation and increased lysozyme resistance. This review highlights how activity of σ is controlled.