To estimate the minimal gene set required to sustain bacterial life in nutritious conditions, we carried out a systematic inactivation of Bacillus subtilis genes. Among Ϸ4,100 genes of the organism, only 192 were shown to be indispensable by this or previous work. Another 79 genes were predicted to be essential. The vast majority of essential genes were categorized in relatively few domains of cell metabolism, with about half involved in information processing, one-fifth involved in the synthesis of cell envelope and the determination of cell shape and division, and one-tenth related to cell energetics. Only 4% of essential genes encode unknown functions. Most essential genes are present throughout a wide range of Bacteria, and almost 70% can also be found in Archaea and Eucarya. However, essential genes related to cell envelope, shape, division, and respiration tend to be lost from bacteria with small genomes. Unexpectedly, most genes involved in the Embden-Meyerhof-Parnas pathway are essential. Identification of unknown and unexpected essential genes opens research avenues to better understanding of processes that sustain bacterial life.

Spore germination, as defined as those events that result in the loss of the spore‐specific properties, is an essentially biophysical process. It occurs without any need for new macromolecular synthesis, so the apparatus required is already present in the mature dormant spore. Germination in response to specific chemical nutrients requires specific receptor proteins, located at the inner membrane of the spore. After penetrating the outer layers of spore coat and cortex, germinant interacts with its receptor: one early consequence of this binding is the movement of monovalent cations from the spore core, followed by Ca2+ and dipicolinic acid (DPA). In some species, an ion transport protein is also required for these early stages. Early events – including loss of heat resistance, ion movements and partial rehydration of the spore core – can occur without cortex hydrolysis, although the latter is required for complete core rehydration and colony formation from a spore. In Bacillus subtilis two crucial cortex lytic enzymes have been identified: one is CwlJ, which is DPA‐responsive and is located at the cortex‐coat junction. The second, SleB, is present both in outer layers and at the inner spore membrane, and is more resistant to wet heat than is CwlJ. Cortex hydrolysis leads to the complete rehydration of the spore core, and then enzyme activity within the spore protoplast resumes. We do not yet know what activates SleB activity in the spore, and neither do we have any information at all on how the spore coat is degraded.