[SCAN 10h30] A bacterial umbilical cord

SCAN

Title: A bacterial umbilical cord

Speaker: Adriano O. Henriques

Affilliation: Microbial Development Laboratory

Abstract:

Bacterial endospores (spores for simplicity) are dormant cell types highly resistant to a variety of physical and chemical insults. At the onset of spore differentiation, cells divide asymmetrically to produce two cells with unequal sizes and dissimilar fates: a smaller forespore, or future spore, and a larger mother cell, which is required for spore formation but lyses at the end of the process to release the matures spore. A key event in spore development is the engulfment of the forespore by the mother cell. This process, akin to phagocytosis, produces a free-floating protoplast (the forespore) inside the mother cell, isolated from the surrounding medium. Upon engulfment completion, the forespore is encased in a system of two membranes of opposite polarity, which derive from the initial asymmetric division septum, and which define an intermembrane compartment.

We describe a complex formed by a mother cell protein, H, and a forespore protein, Q, in the human spore-forming intestinal pathogen Clostridium difficile. H and Q localize to the membranes that surround the forespore in a co-dependent manner. We show that H and Q interact in vitro and in vivo, across the inter-membrane space that separates the forespore from the mother cell. We show that H and Q are required for engulfment presumably because of a zipper-like interaction across the forespore membranes. However, following engulfment completion, the H-Q complex has a second function, which is required for forespore stability and late developmental gene expression.

These observations are consistent with a model in which the H-Q complex forms a feeding-tube that allows the mother cell to nurture the forespore maintaining the potential for macromolecular synthesis in this cell. The H-Q complex appears to be a universal feature of endospore-forming bacteria.