Roles of the Bacillus anthracis spore protein ExsK in exosporium maturation and germination.
The Bacillus anthracis spore is the causative agent of the disease anthrax. The outermost structure of the B. anthracis spore, the exosporium, is a shell composed of approximately 20 proteins. The function of the exosporium remains poorly understood and is an area of active investigation. In this study, we analyzed the previously identified but uncharacterized exosporium protein ExsK. We found that, in contrast to other exosporium proteins, ExsK is present in at least two distinct locations, i.e., the spore surface as well as a more interior location underneath the exosporium. In spores that lack the exosporium basal layer protein ExsFA/BxpB, ExsK fails to encircle the spore and instead is present at only one spore pole, indicating that ExsK assembly to the spore is partially dependent on ExsFA/BxpB. In spores lacking the exosporium surface protein BclA, ExsK fails to mature into high-molecular-mass species observed in wild-type spores. These data suggest that the assembly and maturation of ExsK within the exosporium are dependent on ExsFA/BxpB and BclA. We also found that ExsK is not required for virulence in murine and guinea pig models but that it does inhibit germination. Based on these data, we propose a revised model of exosporium maturation and assembly and suggest a novel role for the exosporium in germination.
Severson
Kari M
KM
Department of Microbiology and Immunology, Loyola University Medical Center, Maywood, Illinois 60153, USA.
Mallozzi
Michael
M
Bozue
Joel
J
Welkos
Susan L
SL
Cote
Christopher K
CK
Knight
Katherine L
KL
Driks
Adam
A
D000818:Animals; D000881:Anthrax / Q000382:microbiology; D001408:Bacillus anthracis / Q000737:chemistry / Q000254:growth & development*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006168:Guinea Pigs; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D013170:Spores / Q000737:chemistry / Q000254:growth & development*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014774:Virulence
D001426:Bacterial Proteins; C470593:BclA protein, Bacillus anthracis; C095092:ExsA protein, bacteria; D008562:Membrane Glycoproteins; D015534:Trans-Activators