Essence of life: essential genes of minimal genomes.

Essential genes are absolutely required for cell survival. Determination of the universal minimal set of genes needed to sustain life is, therefore, expected to contribute greatly to our understanding of life at its simplest level, with applications in medicine and synthetic biology. The search for the minimal genome has led to the identification of often variable gene sets. We argue here that, based on the outcome of these analyses, it is becoming increasingly evident that some genes, and the functions encoded by them, are absolutely necessary for the survival of any living entity, whereas others can be omitted. We also examine ways of determining the minimal genome and discuss possible practical applications of a minimal cell.