Organization and dynamics of the SpoVAEa protein, and its surrounding inner membrane lipids upon germination of Bacillus subtilis spores

Abstract

AbstractThe SpoVA proteins make up a channel in the inner membrane (IM) of B. subtilis spore. This channel responds to signals from activated germinant receptors (GRs), and allows release of Ca2+-DPA from the spore core during germination. In the current work, we studied the location and dynamics of SpoVAEa in dormant spores. Notably, the SpoVAEa-SGFP2 proteins were present in a single spot in spores, similar to the complex formed by all GRs. However, while the GRs’ spot remains in one location, the SpoVAEa-SGFP2 spot in the IM moved randomly with high frequency. The dynamics of the SpoVAEa-SGFP2 and its surrounding IM region as stained by fluorescent dyes were also tracked during spore germination, as the dormant spore IM appeared to have an immobile germination related functional microdomain. This microdomain disappeared around the time of appearance of a germinated spore, the loss of fluorescence of the IM by fluorescent dyes, as well as the appearance of SpoVAEa-SGFP2 peak fluorescent intensity occurred in parallel. These observed events were highly related to the rapid phase darkening, which is considered as the Ca2+DPA rapid release. We also tested the response of SpoVAEa and the IM to thermal treatments at 40-80°C. Heat treatment triggered an increase of green autofluorescence, which is speculated to be due to coat protein denaturation, and 80°C treatments induce the appearance of phase-grey-like spores. These spores presumably have a similar intracellular physical state as the phase grey spores detected in the germination but lack the functional proteins for further germination events.