Minimal genome

The concept of minimal genome assumes that genomes can be reduced to a bare minimum, given that they contain many non-essential genes of limited or situational importance to the organism. Therefore, if a collection of all the essential genes were put together, a minimum genome could be created artificially in a stable environment. By adding more genes, the creation of an organism of desired properties is possible. The concept of minimal genome arose from the observations that many genes do not appear to be necessary for survival. In order to create a new organism a scientist must determine the minimal set of genes required for metabolism and replication. This can be achieved by experimental and computational analysis of the biochemical pathways needed to carry out basic metabolism and reproduction. A good model for a minimal genome is Mycoplasma genitalium, the organism with the smallest known genome. Most genes that are used by this organism are usually considered essential for survival; based on this concept a minimal set of 256 genes has been proposed.

Many naturally occurring bacteria have reduced genomes even though they may not be reduced to the bare minimum. Although these genomes are thus not "minimal", they are good models for genome reduction and thus "minimal genomes". Genome reduction occurs most commonly in endosymbiotic, parasitic or pathogenic bacteria that live in their hosts. The host provides most of the nutrients such bacteria require, hence the bacteria do not need the genes for producing such compounds themselves. Examples include species of Buchnera, Chlamydia, Treponema, Mycoplasma, and many others. One of the most reduced genomes in free-living bacteria has been found in Pelagibacter ubique which encodes 1,354 proteins. Mycoplasma genitalium has been used as a prime model for minimal genomes. It is a human urogenital pathogen which has the smallest genome of size 580 kb and it consists of only 482 protein-coding genes.

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