Essential gene
![Essential genes in Mycobacterium tuberculosis H37Rv as found by using transposons which insert in random positions in the genome. If no transposons are found in a gene, the gene is most likely essential as it cannot tolerate any insertion. In this example, essential heme biosynthetic genes hemA, hemB, hemC, hemD are devoid of insertions. The number of sequence reads (‘‘reads/TA’’) is shown for the indicated region of the H37Rv chromosome. Potential TA dinucleotide insertions sites are indicated. Image from Griffin et al. 2011.[15]](/uploads/202501/11/Transposon_insertions_and_next_generation_sequencing_map_essential_genes_in_Mycobacterium_tuberculosis3552.png)
![Conservation of essential genes in bacteria, adapted from [62]](/uploads/202501/11/Conservation_of_essential_genes3552.png)
Essential genes are those genes of an organism that are thought to be critical for its survival. However, being essential is highly dependent on the circumstances in which an organism lives. For instance, a gene required to digest starch is only essential if starch is the only source of energy. Recently, systematic attempts have been made to identify those genes that are absolutely required to maintain life, provided that all nutrients are available. Such experiments have led to the conclusion that the absolutely required number of genes for bacteria is on the order of about 250-300. These essential genes encode proteins to maintain a central metabolism, replicate DNA, translate genes into proteins, maintain a basic cellular structure, and mediate transport processes into and out of the cell. Most genes are not essential but convey selective advantages and increased fitness.