Abstract
Bacterial endospores exhibit extreme resistance to most conditions that rapidly kill other life forms, remaining viable in this dormant state for centuries or longer. While the majority of Bacillus subtilis dormant spores germinate rapidly in response to nutrient germinants, a small subpopulation termed superdormant spores are resistant to germination, potentially evading antibiotic and/or decontamination strategies. In an effort to better understand the underlying mechanisms of superdormancy, membrane-associated proteins were isolated from populations of B. subtilis dormant, superdormant, and germinated spores, and the relative abundance of 11 germination-related proteins was determined using multiple-reaction-monitoring liquid chromatography-mass spectrometry assays. GerAC, GerKC, and GerD were significantly less abundant in the membrane fractions obtained from superdormant spores than those derived from dormant spores. The amounts of YpeB, GerD, PrkC, GerAC, and GerKC recovered in membrane fractions decreased significantly during germination. Lipoproteins, as a protein class, decreased during spore germination, while YpeB appeared to be specifically degraded. Some protein abundance differences between membrane fractions of dormant and superdormant spores resemble protein changes that take place during germination, suggesting that the superdormant spore isolation procedure may have resulted in early, non-committal germination-associated changes. In addition to low levels of germinant receptor proteins, a deficiency in the GerD lipoprotein may contribute to heterogeneity of spore germination rates. Understanding the reasons for superdormancy may allow for better spore decontamination procedures.