Genome Sequencing Essay Research Paper Genome SequencingMicrobiology

Genome Sequencing Essay, Research Paper

Genome Sequencing

Microbiology has entered the realm of genome sequencing. This biological revolution is opening up new dimensions in our view of life.

In 1995, a report on the entire DNA sequence for the genome of the bacteria Haemophilus influenzae was published . Although the genomes for a number of viruses had been completed before this, H. influenzae was the first free-living organism to have it’s genome sequenced, and as such, this report remains a biological milestone. Since then, the entire genome sequences for over 10 microorganisms have been compiled and released and more are on their way. The completed microbial genomes include:

Haemophilus influenzae finished 1995

Mycoplasma genitalium finished 1995

Methanococcus jannaschii finished 1996

Synechocystis sp. finished 1996

Mycoplasma pneumoniae finished 1996

Saccharomyces cerevisiae finished 1997

Helicobacter pylori finished 1997

Escherichia coli finished 1997

Bacillus subtilis finished 1997

Archaeoglobus fulgidus finished 1997

The benefits of complete genome sequencing projects include a greater understanding of the organisms being sequenced and acknowledgment of the minimum complement of genes necessary for a free-living organism. Of the organisms that have already had their genomes sequenced, a number are of particular importance. For example, Mycoplasma genitalium has a complete nucleotide sequence that is only 580,070 base pairs long, and as such, is believed to be the smallest genome of any free-living organism. Because of it’s unique size, this genome presents a way of studying a minimal functional gene set. In addition, complete genome sequencing projects are currently being carried out on a number of microbial pathogens in an attempt to better understand them. The inference of molecular structures, in particular genome sequences, have direct practical consequences in clinical microbiology. Data and analyses of clinically important microorganisms are being used to develop molecular diognostics as well as to guide research in the nature of these organisms. Information obtained from sequencing is also being used to provide enzymes for biotechnical and industrial applications.

The impact that genome sequencing has had, and will have, on our view of life only begins here. It appears that the time has come to move formal taxonomy and phylogenetic classification into line with the system emerging from molecular data.

Prior to the 1960’s, evolutionary study had been confined to multicellular eucaryotes whose histories, at best, only cover about 20% of the total evolutionary time span. Plants and animals have complex morphologies, which served as the basis for their phylogenetic classification. In contrast, bacteria have morphologies that are too simple to be used in this way. Many early microbiologists avoided the area of phylogenetic classification for this reason, despite the fact that the history of the microbial world spans most of the Earth’s existence. Those who did study the discipline created distorted schemes that are now under review.

Since the 1950’s, molecular studies have been used to determine evolutionary relationships, although microbiology remained blind to the potential of this unique approach until rRNA sequences were shown to provide a key to procaryotic phylogeny in the 1970’s. It would appear that genome sequencing has advanced the science of phylogenetic classification even further.

The failing view of the organisation of life was that all living things were either plant or animal in nature. In 1990, a proposal for a new, natural system of organisms was published, based on the rRNA sequencing revolution. The more recent genome sequencing era has supported this original proposal, and as a result three domains of life are currently recognised; Archaea, Bacteria, and Eucarya, as shown in the universal phylogenetic tree below.

When the first archaeal genome (Methanococcus jannaschii) was sequenced in 1996, it was found that only 44% of the genes were familiar . This phenomenal discovery justified the creation of the three domains, since all are too dissimilar to be included in the same kingdom. It is only on the molecular level that we are able to see the living world divide into three distinct primary groups. For every characterised molecular system there is a characteristic eucaryotic, bacterial and archaeal version, which all members of each particular group share. Genome sequencing ventures are making the recognition of these characteristic systems much easier, as well as making it possible to compare the systems across the three domains.

The discovery that the archaea were in fact a distinct group of organisms from the bacteria challenged the long-standing eucaryote-procaryote dichotomy that has dominated our view of life since it’s proposal in the 1930’s . It has long been recognised that this eucaryote-procaryote scheme was in need of review. While the eucaryotic form of cellular organisation defines a proper phylogenetic unit, procaryotes are only united as a class by their lack of the characteristics that define the eucaryotic cell. As such, the procaryotic definition is a negative one that offers no meaningful phylogenetic information. In the 1950’s it became feasible to

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