Investigation of sporulation in the Desulfotomaculum genus: a genomic comparison with the genera Bacillus and Clostridium

The genus Desulfotomaculum, belonging to the Firmicutes, comprises strictly anaerobic and endospore-forming bacteria capable of dissimilatory sulfate reduction. These microorganisms are metabolically versatile and are widely distributed in the environment. Spore formation allows them to survive prolonged environmental stress. Information on the mechanism of sporulation in Desulfotomaculum species is scarce. Herein, this process was probed from a genomic standpoint, using the Bacillus subtilis model system as a reference and clostridial sporulation for comparison. Desulfotomaculum falls somewhere in between the Bacillus and Clostridium in terms of conservation of sporulation proteins. Furthermore, it showcased the conservation of a core regulatory cascade throughout genera, while uncovering variability in the initiation of sporulation and the structural characteristics of spores from different genera. In particular, while in Clostridium species sporulation is not initiated by a phosphorelay, Desulfotomaculum species harbour homologues of the B.subtilis proteins involved in this process. Conversely, both Clostridium and Desulfotomaculum species conserve very few B.subtilis structural proteins, particularly those found in the outer layers of the spore. Desulfotomaculum species seem to share greater similarity to the outer layers of Clostridium difficile.