The search for essential genes

The bacterial genomic era began with the publication of the chromosomal sequence of Haemophilus influenzae. As few of the observed genes had been examined experimentally, functional assignments were made by comparative analysis and for many genes no annotation could be made. This mini-review briefly describes the genomic-scale experimental approaches being used to identify genes required for the growth of microorganisms. Identifying 'essential genes', the simplest possible annotation for the unknown open reading frames, is important for antibacterial and antifungal research and is a first step to defining the minimum functional requirement for autonomous growth.