Resuscitation-promoting factor (Rpf) terminates dormancy among diverse soil bacteria

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Abstract
Microorganisms often inhabit environments that are suboptimal for growth and reproduction. To survive when challenged by such conditions, individuals may engage in dormancy where they enter a metabolically inactive state. For this persistence strategy to confer an evolutionary advantage, microorganisms must be able to resuscitate and reproduce when conditions improve. Among bacteria in the phylum Actinomycetota, dormancy can be terminated by resuscitation-promoting factor (Rpf), an exoenzyme that hydrolyzes glycosidic bonds in the peptidoglycan of the cell wall. We characterized Rpf from Micrococcus KBS0714, a bacterium isolated from agricultural soil. Compared to previous studies, the Rpf elicited activity at relatively high concentrations, yet demonstrated high substrate affinity. Site-directed mutations at conserved catalytic sites significantly reduced or abolished resuscitation, as did the deletion of repeating motifs in a lectin-encoding linker region. We then tested the effects of recombinant Rpf from Micrococcus KBS0714 on a diverse set of dormant soil bacteria. Patterns of resuscitation mapped onto strain phylogeny, which reflected core features of the cell envelope. Additionally, the direction and magnitude of the Rpf effect were associated with functional traits, in particular, aspects of the moisture niche and biofilm production, which are critical for understanding persistence and resuscitation during dormancy. These findings expand our understanding of how Rpf may affect seed-bank dynamics and have implications for the diversity and functioning of soil ecosystems.
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