title: Localization and assembly of proteins comprising the outer structures of the Bacillus anthracis spore.
abstract: Bacterial spores possess a series of concentrically arranged protective structures that contribute to dormancy, survival and, ultimately, germination. One of these structures, the coat, is present in all spores. In Bacillus anthracis, however, the spore is surrounded by an additional, poorly understood, morphologically complex structure called the exosporium. Here, we characterize three previously discovered exosporium proteins called ExsFA (also known as BxpB), ExsFB (a highly related paralogue of exsFA/bxpB) and IunH (similar to an inosine-uridine-preferring nucleoside hydrolase). We show that in the absence of ExsFA/BxpB, the exosporium protein BclA accumulates asymmetrically to the forespore pole closest to the midpoint of the sporangium (i.e. the mother-cell-proximal pole of the forespore), instead of uniformly encircling the exosporium. ExsFA/BxpB may also have a role in coat assembly, as mutant spore surfaces lack ridges seen in wild-type spores and have a bumpy appearance. ExsFA/BxpB also has a modest but readily detected effect on germination. Nonetheless, an exsFA/bxpB mutant strain is fully virulent in both intramuscular and aerosol challenge models in Guinea pigs. We show that the pattern of localization of ExsFA/BxpB-GFP is a ring, consistent with a location for this protein in the basal layer of the exosporium. In contrast, ExsFB-GFP fluorescence is a solid oval, suggesting a distinct subcellular location for ExsFB-GFP. We also used these fusion proteins to monitor changes in the subcellular locations of these proteins during sporulation. Early in sporulation, both fusions were present throughout the mother cell cytoplasm. As sporulation progressed, GFP fluorescence moved from the mother cell cytoplasm to the forespore surface and formed either a ring of fluorescence, in the case of ExsFA/BxpB, or a solid oval of fluorescence, in the case of ExsFB. IunH-GFP also resulted in a solid oval of fluorescence. We suggest the interpretation that at least some ExsFB-GFP and IunH-GFP resides in the region between the coat and the exosporium, called the interspace.
authors.affiliation: Department of Microbiology and Immunology, Loyola University Medical Center, Maywood, IL 60153, USA.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Giorno
authors.affiliation: Department of Microbiology and Immunology, Loyola University Medical Center, Maywood, IL 60153, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Mallozzi
authors.affiliation: Bacteriology Division, United States Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011, USA.
authors.forename: Joel
authors.initials: J
authors.lastname: Bozue
authors.affiliation: Bacteriology Division, United States Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011, USA.
authors.forename: Krishna-Sulayman
authors.initials: KS
authors.lastname: Moody
authors.affiliation: Department of Microbiology and Immunology, Loyola University Medical Center, Maywood, IL 60153, USA.
authors.forename: Alex
authors.initials: A
authors.lastname: Slack
authors.affiliation: Department of Biological, Chemical, and Physical Sciences, Illinois Institute of Technology, Chicago, IL 60616, USA.
authors.forename: Dengli
authors.initials: D
authors.lastname: Qiu
authors.affiliation: Department of Biological, Chemical, and Physical Sciences, Illinois Institute of Technology, Chicago, IL 60616, USA.
authors.forename: Rong
authors.initials: R
authors.lastname: Wang
authors.affiliation: Headquarters, United States Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011, USA.
authors.forename: Arthur
authors.initials: A
authors.lastname: Friedlander
authors.affiliation: Bacteriology Division, United States Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Welkos
authors.affiliation: Department of Microbiology and Immunology, Loyola University Medical Center, Maywood, IL 60153, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Driks