FIG. 6.

Outgrowth of untreated and heat-treated spores. Ninety-nine percent of strain PS533 spores (wild type) were killed by moist-heat treatment at 87 to 90°C. The spores were separated by equilibrium density gradient centrifugation; the spores in the lower, denser band were isolated, and untreated spores and spores from the lower band were germinated or outgrown in LB medium plus l-alanine as described in Materials and Methods. After incubation in LB medium plus l-alanine for either 75 min (untreated spores) or 5 h (spores from the lower band), aliquots were harvested, fixed with formaldehyde, suspended in 200 μl of PBS, and examined by DIC microscopy as described in Materials and Methods. The images of untreated spores (a to c) and spores from the lower band (d) are all at the same magnification. Scale bar, 20 μm.