The role of the exosporium in the environmental distribution of anthrax



Ezra Linley, Cardiff School of Pharmacy and Pharmaceutical Sciences, Cardiff University, King Edward VII Avenue, Cardiff CF10 3NB, UK. E-mail:



To determine the contribution of the exosporium, the outer layer of the Bacillus anthracis spore, to soil attachment. Persistence of spores in soil and their ability to infect animals has been linked to a range of factors which include the presence of organic material and calcium (OMC), pH > 6·0, temperatures above 15·5°C and cycles of local flooding which are thought to transport buried spores to the surface.

Methods and Results

The ability of wild type (exosporium +ve) and sonicated (exosporium −ve) spores to bind to soils which differed in their composition was determined using a flow-through soil column-based method. A statistically significant difference (P < 0·05) in the binding of wild type spores was observed with spores adhering more firmly to the soil with the highest OMC content. We also found that the removal of the exosporium increased the ability of the spore to adhere to both soil types.


Structures within the exosporium affected the ability of B. anthracis spores to bind to different soil types. Not surprisingly, wild type spores adhered to soil which has been shown to favour the persistence of the pathogen.

Significance and Impact of the Study

The ability to persist in and colonise the soil surface is a key requirement of a pathogen which infects grazing animals. By characterising the process involved, we will be better placed to develop strategies to disrupt the infection cycle.