<italic>Bacillus anthracis</italic> endospore germination: An analysis of purine co-germinants, the germination operon <italic>gerH</italic>, and the micro-environments in which <italic>B. anthracis</italic> endospores germinate.

The work presented in this dissertation examines B. anthracis endospore germination by characterizing the roles played by purine nucleosides and gerH in germination, and by using the gerH null strain as a tool to further dissect the germination response pathways present in M&phis; conditioned solutions, serum and soil. Furthermore, the mechanisms by which germinants become available to endospores was investigated, as were the different micro-environments in which B. anthracis can germinate. The tri-cistronic operon gerH was identified, with high homology to gerI, an ortholog necessary for inosine-dependent B. cereus endospore germination. B. anthracis endospores did not germinate in inosine alone, but germination was triggered by inosine in binary combination with amino acid co-germinants grouped into two distinct germination response pathways: inosine-His and purine-Ala. Purines can be substituted for inosine in the inosine-Ala pathway, which includes inosine-Ser, but not in the inosine-His pathway, which requires gerH. Unlike B. anthracis Sterne endospores, gerH null endospores do not germinate in the presence of macrophages and in macrophage-conditioned media. Germination assays performed in alluvial soil extracts demonstrate for the first time that B. anthracis endospores can germinate in a natural environment outside of a host, and that ex vivo germination utilizes, in part, gerH. This finding re-energizes the discussion of the different ecological niches which may support the germination and growth of B. anthracis.PhDBiological SciencesMicrobiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123976/2/3106184.pd