Minimal genome

The minimal genome concept 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 due to its very small genome size. 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. The minimal genome concept 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 due to its very small genome size. 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. Viruses have the smallest genomes in nature. For instance, bacteriophage MS2 consists of only 3569 nucleotides (single-stranded RNA) and encodes just four proteins. Similarly, among eukaryotic viruses, porcine circoviruses are among the smallest. They encode only 2–3 open reading frames. This concept arose as a result of a collaborative effort between National Aeronautics and Space Administration (NASA) and two scientists: Harold Morowitz and Mark Tourtellotte. In the 1960s, NASA was searching for extraterrestrial life forms, assuming that if they existed they may be simple creatures. While Morowitz, to attract people's attention published about mycoplasmas as being the smallest and simplest self-replicating creatures. The two grouped together and came up with an idea to assemble a living cell from the components of mycoplasmas. Since, mycoplasmas are built with a minimum set of organelles such as: a plasma membrane, ribosomes and a circular double stranded DNA; it was selected as the best candidate for cell reassembly. Morowitz' major idea was to define the entire machinery of mycoplasmas cell in molecular level. He announced that an international effort would help him accomplish this main objective. This entire process was hard work, meanwhile even when papers were being published on the construction of minimal genome; by the 1980s Richard Herrmann's laboratory had successfully managed to fully sequence and genetically characterize the 800kb genome of M. pneumoniae. That small of a genome itself took close to three years of hard work. Later in the 1995s another laboratory located in Maryland the Institute for Genomic Research (TIGR) collaborated with the teams of Johns Hopkins and University of North Carolina. Their organism for genome sequencing was Mycoplasma genitalium consisting of only 580 kb genome, the sequencing of which was done in 6 months.