The SpoIIQ-SpoIIIAH complex of Clostridium difficile controls forespore engulfment and late stages of gene expression and spore morphogenesis

Mol Microbiol. 2016 Apr;100(1):204-28. doi: 10.1111/mmi.13311. Epub 2016 Feb 12.


Engulfment of the forespore by the mother cell is a universal feature of endosporulation. In Bacillus subtilis, the forespore protein SpoIIQ and the mother cell protein SpoIIIAH form a channel, essential for endosporulation, through which the developing spore is nurtured. The two proteins also form a backup system for engulfment. Unlike in B. subtilis, SpoIIQ of Clostridium difficile has intact LytM zinc-binding motifs. We show that spoIIQ or spoIIIAH deletion mutants of C. difficile result in anomalous engulfment, and that disruption of the SpoIIQ LytM domain via a single amino acid substitution (H120S) impairs engulfment differently. SpoIIQ and SpoIIQ(H120S) interact with SpoIIIAH throughout engulfment. SpoIIQ, but not SpoIIQ(H120S) , binds Zn(2+) , and metal absence alters the SpoIIQ-SpoIIIAH complex in vitro. Possibly, SpoIIQ(H120S) supports normal engulfment in some cells but not a second function of the complex, required following engulfment completion. We show that cells of the spoIIQ or spoIIIAH mutants that complete engulfment are impaired in post-engulfment, forespore and mother cell-specific gene expression, suggesting a channel-like function. Both engulfment and a channel-like function may be ancestral functions of SpoIIQ-SpoIIIAH while the requirement for engulfment was alleviated through the emergence of redundant mechanisms in B. subtilis and related organisms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Clostridioides difficile / physiology*
  • Gene Expression Regulation, Bacterial*
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Sequence Deletion
  • Spores, Bacterial*


  • Bacterial Proteins