Role of the Spore Coat Layers in <i>Bacillus subtilis</i> Spore Resistance to Hydrogen Peroxide, Artificial UV-C, UV-B, and Solar UV Radiation

TLDR

Bacillus subtilis spores have a thick protein coat composed of an outer electron‑dense layer and an inner lamellate layer that protects them from lysozyme and other sporicidal agents. This study investigates how the outer and inner coat layers contribute to resistance against hydrogen peroxide and various UV treatments. The authors examined gerE36 and cotE::cat mutants, alone and in combination, to assess the role of each coat layer in spore resistance. Mutants lacking the inner coat layer (gerE36) were highly sensitive to H₂O₂, lysozyme, and UV‑B/solar UV, whereas mutants lacking the outer coat layer (cotE::cat) were more resistant to UV, and double mutants resembled gerE36, indicating the inner coat layer is critical for UV resistance.

Abstract

Spores of Bacillus subtilis possess a thick protein coat that consists of an electron-dense outer coat layer and a lamellalike inner coat layer. The spore coat has been shown to confer resistance to lysozyme and other sporicidal substances. In this study, spore coat-defective mutants of B. subtilis (containing the gerE36 and/or cotE::cat mutation) were used to study the relative contributions of spore coat layers to spore resistance to hydrogen peroxide (H(2)O(2)) and various artificial and solar UV treatments. Spores of strains carrying mutations in gerE and/or cotE were very sensitive to lysozyme and to 5% H(2)O(2), as were chemically decoated spores of the wild-type parental strain. Spores of all coat-defective strains were as resistant to 254-nm UV-C radiation as wild-type spores were. Spores possessing the gerE36 mutation were significantly more sensitive to artificial UV-B and solar UV radiation than wild-type spores were. In contrast, spores of strains possessing the cotE::cat mutation were significantly more resistant to all of the UV treatments used than wild-type spores were. Spores of strains carrying both the gerE36 and cotE::cat mutations behaved like gerE36 mutant spores. Our results indicate that the spore coat, particularly the inner coat layer, plays a role in spore resistance to environmentally relevant UV wavelengths.