Formaldehyde kills spores of Bacillus subtilis by DNA damage and small, acid-soluble spore proteins of the alpha/beta-type protect spores against this DNA damage.

Killing of wild-type spores of Bacillus subtilis with formaldehyde also caused significant mutagenesis; spores (termed alpha-beta-) lacking the two major alpha/beta-type small, acid-soluble spore proteins (SASP) were more sensitive to both formaldehyde killing and mutagenesis. A recA mutation sensitized both wild-type and alpha-beta- spores to formaldehyde treatment, which caused significant expression of a recA-lacZ fusion when the treated spores germinated. Formaldehyde also caused protein-DNA cross-linking in both wild-type and alpha-beta- spores. These results indicate that: (i) formaldehyde kills B. subtilis spores at least in part by DNA damage and (b) alpha/beta-type SASP protect against spore killing by formaldehyde, presumably by protecting spore DNA.