Atomic force microscopy study of germination and killing of Bacillus atrophaeus spores

Bacterial spores such as Bacillus atrophaeus are one of the most resistant life forms known and are extremely resistant to chemical and environmental factors in the dormant state. During germination, as bacterial spores progress towards the vegetative state, they become susceptible to anti-sporal agents. B. atrophaeus spores were exposed to the non-nutritive germinant dodecylamine (DDA), a cationic surfactant that can also be used as a killing agent, for up to 60 min, or to the nutrient germinant L-alanine. In kinetic studies, 99% of the spores were killed within 5 min of exposure to DDA. Atomic force microscopy (AFM) can be used as a sensitive tool to assess how the structure of the spore coat changes upon exposure to germinants or killing agents. Changes in cell height and roughness over time of exposure to DDA were examined using AFM. DDA caused the spore height to decrease by >50%, which may have been due to a partial breakdown of the spore coat. Treatment of B. atrophaeus with the nutrient germinant resulted in a decrease in height of spores after 2 h of incubation, from 0.7 +/- 0.1 microm to 0.3 +/- 0.2 microm. However, treatment with L-alanine did not change the surface roughness of the spores, indicating that the changes that occur during germination take place underneath the spore coat. We propose that exposure to DDA at high concentrations causes pores to form in the coat layer, killing B. atrophaeus without the need to fully germinate spores.