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.

Systematic inactivation of Bacillus subtilis genes has previously revealed that 271 are indispensable for growth. In the present study, 11 of these (yacA, ydiB, ydiC, ykqC, ylaN, yloQ, ymdA, yneS, yqeI, yqjK and ywlC) were identified as genes encoding proteins of unknown function. By analysing the effects of protein depletion, and examining the subcellular localization of these proteins, a start has been made in elucidating their functions. It was found that four of these genes (ydiB, yloQ, yqeI and ywlC) were not required for B. subtilis viability. Analysis of the localization of YkqC suggests that it co-localizes with ribosomes, and it is proposed that it is involved in processing either rRNA or specific mRNAs when they are associated with the ribosome. The results suggest that other novel essential proteins may be involved in lipid synthesis and control of cell wall synthesis.