Forespore engulfment mediated by a ratchet-like mechanism.
A key step in bacterial endospore formation is engulfment, during which one bacterial cell engulfs another in a phagocytosis-like process that normally requires SpoIID, SpoIIM, and SpoIIP (DMP). We here describe a second mechanism involving the zipper-like interaction between the forespore protein SpoIIQ and its mother cell ligand SpoIIIAH, which are essential for engulfment when DMP activity is reduced or SpoIIB is absent. They are also required for the rapid engulfment observed during the enzymatic removal of peptidoglycan, a process that does not require DMP. These results suggest the existence of two separate engulfment machineries that compensate for one another in intact cells, thereby rendering engulfment robust. Photobleaching analysis demonstrates that SpoIIQ assembles a stationary structure, suggesting that SpoIIQ and SpoIIIAH function as a ratchet that renders forward membrane movement irreversible. We suggest that ratchet-mediated engulfment minimizes the utilization of chemical energy during this dramatic cellular reorganization, which occurs during starvation.
Broder
Dan H
DH
Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
Pogliano
Kit
K
D001412:Bacillus subtilis / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000235:genetics; D008561:Membrane Fusion; D020409:Molecular Motor Proteins / Q000235:genetics / Q000378:metabolism*; D009113:Muramidase; D009154:Mutation; D010457:Peptidoglycan / Q000378:metabolism*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013171:Spores, Bacterial / Q000502:physiology
D001426:Bacterial Proteins; D020409:Molecular Motor Proteins; D010457:Peptidoglycan; D011993:Recombinant Fusion Proteins; C030069:spore-specific proteins, Bacillus; D049452:Green Fluorescent Proteins; D009113:Muramidase