Germination and outgrowth of Bacillus thuringiensis and Bacillus alvei spores viewed by scanning electron and phase-contrast microscopy

Abstract

Germination and outgrowth of Bacillus thuringiensis and Bacillus alvei spores were observed by scanning electron (SEM) and phase-contrast microscopy. Germination, seen in phase-contrast as the loss of retractility of the spore, appears in SEM as a partial collapse of the spore. This collapse parallels the long axis of B. thuringiensis and is perpendicular to that of B. alvei. Outgrowth is initiated when the spore begins to swell. During swelling, the outgrowing spore appears to collapse in SEM and, for B. thuringiensis, becomes gnarled. It then begins to elongate and during the elongation time the parasporal body of B. thuringiensis loses its refractility and swells. B. alvei has no parasporal body. As the cell pushes its way out of the sporangium, the phase-dark parasporal body loses definitive shape; the emerging cell may elaborate an enveloping structure seen only in SEM. This cell then divides into two vegetative cells that also are surrounded by a similar structure. Such an enveloping structure is not seen with B. alvei.