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Investigating the Nature of Bacterial Spores

Final Report Summary - BACTERIAL SPORES (Investigating the Nature of Bacterial Spores)

Upon starvation, the bacterium Bacillus subtilis enters the process of sporulation, culminating in formation of a spore, the most resilient cell type known. Bacterial spores can survive long periods of time and can withstand extremes of heat, radiation, and chemical assault through mechanisms which are poorly understood. The unusual biochemical and biophysical characteristics of the dormant spore make it a challenging biological system to elucidate. Remarkably, dormant spores can rapidly convert back to actively growing cells in a process called germination followed by spore outgrowth. We exploit this robust developmental system to address fundamental questions in spore biology. During the ERC grant period we have made significant progress towards exploring the spore molecular characteristics and achieving our major aims. We developed molecular and cell biological approaches that enable us to explore the nature of spores. By utilizing these methods, we demonstrated that in contrast to current thinking molecular changes are taking place within mature spores. We observed that a few days post sporulation the RNA profile of spores is highly dynamic. In aging spores incubated at high temperatures, the RNA content is globally decreased by active degradation in the course of several days. This degradation might be a strategy exploited by the spore to facilitate its dormancy. On the other hand, in spores kept at low temperatures transcription was evident. Utilizing dynamic proteomic and cell biology analyses we monitored corresponding molecular changes at the protein level. Moreover, we showed that germination is affected by spore age and incubation temperature, implying that spores acquire dissimilar characteristics at a time they are considered dormant. We have further analysed in detail the remarkable spore ability to rapidly revive, by assessing the dynamics of the reviving spore phosphorproteome, by defining a distinct morphological stage during spore revival extending between germination and cell elongation, termed "the ripening period", and by tracking the proteins synthesized during revival. We have also revealed for the first time that protein synthesis is taking place during germination, and identified novel revival specific components that could represent key therapeutic targets for eradicating spore-forming pathogens. Indeed, as part of the ERC project, we designed a drug, termed Relacin, which is able to inhibit bacilli sporulation (patented).
Finally, several other projects have emerged from our research with the most prominent one being the discovery of a novel type of bacterial communication that is mediated by intercellular nanotubes (Dubey and Ben-Yehuda, Cell, 2011), and a collaborative research that defined the localization of mRNA as a cue for gene regulation in bacteria (Nevo-Dinur et al., Science, 2011).