Interference contrast and phase contrast microscopy of sporulation and germination of Bacillus megaterium.

The techniques of Nomarski interference contrast microscopy and phase-contrast microscopy were compared for their utility in monitoring sporulation and germination in Bacillus megaterium. The Nomarski technique permitted rapid and easy delineation of septation and engulfment during sporulation, whereas with phase contrast microscopy these stages were not detected at all. The later stages of sporulation were easily seen by either technique. Thus, of the seven stages of sporulation as recognized by the electron microscopy of thin sections, five can now be routinely detected quantitatively by optical microscopy: septation (stage II), engulfment (stage III), phase-dark forespore (corresponding to cortex formation, stage IV), phase-bright spore in a sporangium (corresponding to coat formation, stage V), and the free spore (stage VII). This means that now only stage I (axial filament) and stage VI (maturation of the refractile spore) require electron microscopy for routine detection. There was no advantage in using Nomarski optics for germination studies.