Binding of small, acid-soluble spore proteins to DNA plays a significant role in the resistance of Bacillus subtilis spores to hydrogen peroxide

Abstract

Dormant spores of Bacillus subtilis which lack the majority of the α/β- type small, acid-soluble proteins (SASP) (termed α- β- spores) that coat the DNA in wild-type spores are significantly more sensitive to hydrogen peroxide than are wild-type spores. Hydrogen peroxide treatment of α- β- spores causes DNA strand breaks more readily than does comparable treatment of wild-type spores, and α- β- spores, but not wild-type spores, which survive hydrogen peroxide treatment have acquired a significant number of mutations. The hydrogen peroxide resistance of wild-type spores appears to be acquired in at least two incremental steps during sporulation. The first increment is acquired at about the time of α/β-type SASP synthesis, and the second increment is acquired approximately 2 h later, at about the time of dipicolinic acid accumulation. During sporulation of the α- β- strain, only the second increment of hydrogen peroxide resistance is acquired. In contrast, sporulation mutants which accumulate α/β-type SASP but progress no further in sporulation acquire only the first increment of hydrogen peroxide resistance. These findings strongly suggest that binding of α/β- type SASP to DNA provides one increment of spore hydrogen peroxide resistance. Indeed, binding of α/β-type SASP to DNA in vitro provides strong protection against cleavage of DNA by hydrogen peroxide.