Dry versus wet dormancy: suspended lives of Bacillus subtilis versus Saccharomyces cerevisiae spores

Dormant microbial spores provide one of the clearest and most extreme examples of how cells can pause life for extended periods and then reliably restart it. Although bacterial and fungal spores are often grouped under “dormancy,” the physical strategies by which they suspend and resume life differ fundamentally. Here, I compare two canonical systems—Bacillus subtilis endospores and Saccharomyces cerevisiae ascospores—using a dynamical-systems framework from a physicist’s perspective. I propose that dormancy is not simply “low metabolism,” but a dynamical reconfiguration that decouples local molecular clocks from a global biological clock while preserving an intrinsic capacity to resume sustained nonequilibrium dynamics, which I refer to as nonequilibrium capacity. Specifically, in B. subtilis spores, “dry dormancy” is enforced by immobilization: dehydration and material constraints suppress appreciable molecular diffusion and reaction fluxes, arresting global biological time by suppressing local molecular clocks. In S. cerevisiae spores, “wet dormancy” appears to be achieved by throttling: spores remain hydrated, retain molecular mobility, and support some slow irreversible processes such as gene expression, yet global biological time remains arrested because, as I propose, local activity fails to propagate into sustained organism-level progression (e.g., growth and division). Together, these comparisons place dry and wet dormancy as distinct regions of a physical design space defined by hydration, molecular mobility, energetic flux, and cross-scale coupling between local activity and global progression, and motivate quantitative models of dormancy and revival dynamics.