Effects of sporulation in an extremely poor medium on Bacillus subtilis spore resistance, germination, and physical properties

ABSTRACT Spores of Bacillus species are metabolically dormant and resistant to many agents but can come back to life in germination triggered by a variety of small molecules; these spore properties vary depending on the conditions and media for spore formation. In the current work, we have compared the properties of Bacillus subtilis spores made in a rich medium and an extremely poor medium. Notably, spores made in the poor liquid medium had lowered resistance to wet heat and somewhat lowered resistance to hydrogen peroxide and formaldehyde. Spores made in the poor liquid medium also have an inner membrane (IM) that is more permeable and fluid compared to the IM in spores made in a rich medium. The poor liquid medium spores also germinated slower than the rich medium spores with several germinant receptor (GR) germinants but faster with the non-GR-dependent germinant dodecylamine. While the reasons for the latter differences are likely the more fluid and permeable IM in the poor medium spores, there were minimal, if any, differences between rich and poor medium spores in their levels of core water or CaDPA, two compounds that alone have major effects on spore resistance properties. These findings provide new information on the resistance and germination properties of spores of B. subtilis . IMPORTANCE Spores of various Bacillus species can cause adverse effects such as food spoilage and some human diseases due to their resistance properties and ability to “come back to life” in spore germination. The reason for these effects has been commonly studied using spores prepared in relatively rich media, and there is a large body of literature on this. However, there have been minimal, if any, studies using spores prepared in an extremely poor medium, as was done in the current work. We believe that the findings in this work provide new insight into mechanisms of spore resistance and their germination.