title: Bacillus spore wet heat resistance and evidence for the role of an expanded osmoregulatory spore cortex.
abstract: Previous work reported that decoated Bacillus cereus spores incubated in 4 mol l(-1) CaCl2 are killed at lower temperatures than spores in water. This wet heat sensitization was suggested to support a role for an osmoregulatory peptidoglycan cortex in spore cores' low water content, and their wet heat resistance. Current work has replicated this finding with spores of B. cereus, Bacillus megaterium and Bacillus subtilis. However, this work found that decoated spores apparently killed at 80°C in 4 mol l(-1) CaCl2 : (i) were recovered on plates containing lysozyme; (ii) lost no dipicolinic acid (DPA) and their inner membrane remained impermeable; (iii) released no DPA upon stimulation with nutrient germinants and could not complete germination; and (iv) released DPA relatively normally upon stimulation with dodecylamine. These results indicate that decoated spores treated with 80°C- 4 mol l(-1) CaCl2 are not dead, but some protein(s) essential for spore germination, most likely germinant receptors, are inactivated by this treatment. Thus, the original finding does not support a role for an osmoregulatory cortex in spore wet heat resistance.
  
  
  CONCLUSIONS
  Bacillus spores' low core water content is a major factor in their wet heat resistance. One suggested mechanism for achieving low spore core water content is osmoregulated expansion of spores' peptidoglycan cortex. Evidence for this mechanism includes a report that decoated Bacillus cereus spores incubated in 4 mol l(-1) CaCl2 exhibit drastically reduced heat resistance. The current work shows that this heat sensitization of decoated spores of three Bacillus species is most likely due to inactivation of some crucial spore germination protein(s), since while treated spores appear dead, their apparent low viability is rescued by triggering spore germination with lysozyme.
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, China.|National Engineering Research Center for Fruit and Vegetable Processing, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture, Beijing, China.|Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, USA.
authors.forename: L
authors.initials: L
authors.lastname: Rao
authors.affiliation: Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, China.|National Engineering Research Center for Fruit and Vegetable Processing, Key Lab of Fruit and Vegetable Processing, Ministry of Agriculture, Beijing, China.
authors.forename: X
authors.initials: X
authors.lastname: Liao
authors.affiliation: Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, USA. setlow@nso2.uchc.edu.
authors.forename: P
authors.initials: P
authors.lastname: Setlow
mesh_terms: D000588:Amines / Q000494:pharmacology; D001409:Bacillus cereus / Q000502:physiology*; D001410:Bacillus megaterium / Q000502:physiology*; D001412:Bacillus subtilis / Q000502:physiology*; D001426:Bacterial Proteins; D002122:Calcium Chloride / Q000494:pharmacology*; D006358:Hot Temperature; D009113:Muramidase / Q000494:pharmacology*; D009997:Osmotic Pressure / Q000502:physiology; D010457:Peptidoglycan / Q000378:metabolism; D010848:Picolinic Acids / Q000378:metabolism; D013171:Spores, Bacterial / Q000502:physiology*; D014867:Water
chemical_list: D000588:Amines; D001426:Bacterial Proteins; D010457:Peptidoglycan; D010848:Picolinic Acids; D014867:Water; D009113:Muramidase; D002122:Calcium Chloride; C004860:dipicolinic acid; C003935:dodecylamine
keywords: Bacillus; spore germination; spore killing; spore resistance; spores