SpoVAF and FigP assemble into oligomeric ion channels that enhance spore germination

Abstract

Bacterial spores can remain dormant for decades yet rapidly germinate and resume growth in response to nutrients. GerA family receptors that sense and respond to these signals have recently been shown to oligomerize into nutrient-gated ion channels. Ion release initiates exit from dormancy. Here, we report that a distinct ion channel, composed of SpoVAF (5AF) and its newly discovered partner protein, YqhR (FigP), amplifies the response. At high germinant concentrations, 5AF/FigP accelerate germination; at low concentrations, this complex becomes critical for exit from dormancy. 5AF is homologous to the channel-forming subunit of GerA family receptors and is predicted to oligomerize around a central pore. 5AF mutations predicted to widen the channel cause constitutive germination during spore formation and membrane depolarization in vegetative cells. Narrow-channel mutants are impaired in germination. A screen for suppressors of a constitutively germinating 5AF mutant identified FigP as an essential cofactor of 5AF activity. We demonstrate that 5AF and FigP interact and colocalize with GerA family receptors in spores. Finally, we show that 5AF/FigP accelerate germination in B. subtilis spores that have nutrient receptors from another species. Our data support a model in which nutrient-triggered ion release by GerA family receptors activates 5AF/FigP ion release, amplifying the response to germinant signals.