The exosporium as passive, non-specific protector
The existence of the exosporium alone protects inner cell structures by masking inflammatory signals in the spore coat, and further contributes to intracellular survival by inhibiting the activity of antibacterial radicals. The exosporium is present in Bacillus anthracis, a spore-forming bacterium, all members of the Bacillus cereus group and some clostridia, such as Clostridium difficile. The latter forms a spore similar in structure to that of the complex B. anthracis. Researchers are working to discover the function of the coat lining structure in the survival of these spores. 'The contribution of the exosporium of Bacillus anthracis to survival' (Roleexosporium) is a project aiming to determine how the exosporium facilitates survival of B. anthracis, contributes to biocide resistance, and also to virulence and in vivo germination. Work on the third objective was undertaken together with colleagues in the US. To date, a fully functional research laboratory for these studies has been established at the UK's Cardiff University. Preliminary studies have successfully characterised the properties of wild-type spores and determined their ability to germinate in response to various triggers. Researchers will compare these results with those obtained in studies of exosporium-deficient spores. Notably, within the first 18 months of the project, Roleexosporium researchers developed a fully defined minimal medium capable of supporting the growth of B. anthracis. In investigating how exosporium contributes to biocide resistance, preliminary studies found that sonicated (physically altered) spores were far more sensitive to the chlorine-releasing biocide Chlorox than their wild-type counterparts. This suggests that the exosporium acts as a physical barrier and reacts with the biocide before it can invade molecules in the spore's core. Other studies have been undertaken to characterise the intracellular survival of B. anthracis spores after uptake by macrophages, white blood cells that work to eradicate pathogens. Performed in collaboration with US colleagues, this work highlights the important role that bacterial arginase has in directing the immune response of infected cells. The study is described in a manuscript that has been accepted for publication by the Current Microbiology journal.
