Having ascertained that ungerminated spores of C. sporogenes
possess an aperture or sporiduct at the terminal of the exosporium,
we tested the hypothesis that the newly formed cell would
emerge through this structure. C. sporogenes spores were incubated
in anaerobic TY medium plus L-alanine and L-lactate which
had previously been shown to be effective conditions for germination
and outgrowth of C. sporogenes spores (Brunt et al., 2014).
Samples were taken periodically for scanning electron microscopy.
However, emergence and outgrowth were not synchronous
and samples contained spores and cells at various stages of
morphological development. Emergence of the newly formed cell
occurred through the preformed aperture or sporiduct of the
spore (Fig. 3) forcing the aperture to distend and the sporiduct to
stretch (Fig. 3a and c). As the cell continued to elongate, emerging
cells had remnants of presumably the spore cell wall or cortical
elements attached (Fig. 3b). In general the cells continued to grow
and elongate from within the exosporium case (Fig. 3d and e).
Moreover, a large proportion of these emerging cells were already
showing septum formation (Fig. 3d and e). A comparable study
with B. anthracis had previously shown that the outgrowing
expanding single cell bursts from its coat and exosporium case
through a preformed cap in the exosporiumbefore elongation and
division (Steichen et al., 2005, 2007).