In Pursuit of Protein Targets: Proteomic Characterization of Bacterial Spore Outer Layers

Bacillus cereus, responsible for food poisoning,
and Clostridium difficile, the causative agent of Clostridium difficile-associated diarrhea (CDAD), are both
spore-forming pathogens involved in food spoilage, food intoxication,
and other infections in humans and animals. The proteinaceous coat
and the exosporium layers from spores are important for their resistance
and pathogenicity characteristics. The exosporium additionally provides
an ability to adhere to surfaces eventually leading to spore survival
in food. Thus, studying these layers and identifying suitable protein
targets for rapid detection and removal of spores is of the utmost
importance. In this study, we identified 100 proteins from B. cereus spore coat, exosporium and 54 proteins from the C. difficile coat insoluble protein fraction. In an attempt
to define a universal set of spore outer layer proteins, we identified
11 superfamily domains common to the identified proteins from two Bacilli and one Clostridium species. The
evaluated orthologue relationships of identified proteins across different
spore formers resulted in a set of 13 coat proteins conserved across
the spore formers and 12 exosporium proteins conserved in the B. cereus group, which could be tested for quick and easy
detection or targeted in strategies aimed at removal of spores from
surfaces.