Atomic force microscopy of Bacillus spore surface morphology

Bacillus spore surface morphology was imaged with atomic force microscopy (AFM) to determine if characteristic surface features could be used to distinguish between four closely related species; Bacillus anthracis Sterne strain, Bacillus thuringiensis var. kurstaki, Bacillus cereus strain 569, and Bacillus globigii var. niger. AFM surface height images showed an irregular topography across the curved upper surface of the spores. Phase images showed a superficial grain structure with different levels of phase contrast and significant differences in average surface morphologies among the four species. Although spores of the same species showed similarities, there was significant variability within each species. Overall, AFM revealed that spore surface morphology is rich with information, which can be used to distinguish a sample of about 20 spores from a similar number of spores of closely related species. Statistical analysis of spore morphology from a combination of amplitude and phase images for a small sample allows differentiation between, B. anthracis and its close relatives.