Bioenergetic metabolism restarts alongside germinant sensing and hydration in bacterial spore germination

Bacterial spore germination transforms spores from dormant bodies to vegetative cells. Initiation of germination or spore rehydration can proceed without exogenous energy sources, so bioenergetic processes in germination have been overlooked, despite many germinants being energy sources, such as sugars. Here, we apply remission spectroscopy to noninvasively measure the energy-transducing electron-transport chain of intact spores during germination. In Bacillus megaterium and Bacillus subtilis, we find energisation of cytoplasmic metabolism and the electron transport chain occurs early in germination, before or alongside rehydration. The aa3-type oxidases (Qox, Cta) accumulate nonradical ferryl intermediates of their catalytic cycle demonstrating that the electron-transport chain is operating in a regime of high membrane potential. The Yth isoform of the bd oxidase is found in abundance in both organisms, functioning to allow rapid electron transfer to O2 when the aa3-type oxidases are hindered, establishing a new role for this enzyme beyond O2-scavenging. Deletion of Yth slows rehydration, directly linking bioenergetic processes to germination. Our data lead us to propose a powered germination model, where the Ger-mediated signalling cascade and bioenergetic processes occur simultaneously and semi-independently.