Department Of Microbiology

All living organisms include DNA. This superb macromolecule encodes all of the information needed to program the cell's activities together with reproduction, metabolism and other specialized functions. DNA is comprised of two strands of deoxynucleotides. Each deoxynucleotide contains a phosphate, a 5-carbon sugar (2-deoxyribose) and one of four nitrogenous bases: adenine, cytosine, thymine or guanine. The phosphate and sugar make up the spine of each strand of DNA, while the bases are responsible for holding the two strands together via hydrogen bonds in a construction called the double helix (see determine). The order of the bases in a DNA strand contains the coded genetic info. All the DNA found in an organism is collectively referred to as the genome. The human genome is comprised of 23 pairs of linear chromosomes, and approximately 3000 megabases (Mb) of DNA, while the genome of the bacterium Escherichia coli consists of a single 4.6 Mb circular chromosome. By studying the genomes of micro organism we're in a position to better understand their metabolic capabilities, their capacity to trigger disease and also their capacity to survive in extreme environments.Most of the nicely-studied bacterial mannequin organisms, such as E. coli, have a single circular chromosome. Nevertheless, advances in molecular genetics have shown that micro organism possess extra complex arrangements of their genetic materials than only a single circular chromosome per cell. Some bacterial genomes are comprised of a number of chromosomes and/or plasmids and many bacteria harbor multiple copies of their genome per cell. The next are a couple of examples of micro organism with unusual genomes.

Genome Terminology

Kb/Mb - A kilobase (Kb) is 1000 bases of DNA, while a megabase (Mb) is 1,000,000 bases. Circular Chromosome ·The DNA is arranged in a closed circle, which is negatively supercoiled allowing for the compact nature of many bacterial genomes. Linear Chromosome · A non-closed chromosome, which has inverted repeats at the ends, just like teleomeres in eukaryotic chromosomes. Plasmid · Additional-chromosomal DNA which replicates independently of the chromosome and regulates its own replication. Megaplasmid · A really large plasmid ranging in measurement from 100- 1700 Kb.

Deinococcus radiodurans

Deinococcus radiodurans was first discovered in 1956 by Arthur W. Anderson. While inspecting spoiled meat, he observed reddish colonies forming although the meat had been sterilized with megarads of radiation! This radiation resistant organism was given the identify Deinococcus radiodurans - which literally means "unusual berry that withstands radiation." Deinococcus radiodurans is in a position to survive radiation exposure as much as 1,500,000 rads! That is 3,000 times higher than the quantity of radiation exposure that will kill a human. Ionizing radiation makes double-strand breaks within the DNA. Cells have mechanisms to repair these lesions but if too many breaks are made, stitching together the DNA in the best order can overwhelm the cell·s DNA repair mechanisms. By some means, D. radiodurans has the power to restore a shattered genome. makeup tutorial for beginners of D. radiodurans is unusual in that it is composed of two chromosomes, a megaplasmid and a small plasmid. In addition, when D. radiodurans cells divide they don't utterly separate from each other instantly and so cells often exist as tetrads (see photo for instance). While the mechanisms by which D. radiodurans is ready to survive excessive doses of radiation are still below investigation, it's hypothesized that by having a number of copies of its genome and by genetic change between cells in a tetrad, D. radiodurans is able to deal with multiple DNA breaks induced by high levels of radiation.

Azotobacter vinelandii

Azotobacter vinelandii is a large, soil-dwelling, obligate aerobic bacterium capable of fixing nitrogen. In addition, A. vinelandii can metabolize a lot of carbohydrates, natural acids and alcohols. The number of genomes in an individual cell is dependent upon the expansion stage of the cells. Throughout exponential growth, A. vinelandii cells sometimes include 2 to 4 copies of their chromosome. Nonetheless, during stationary part, the variety of chromosomes in an individual cell can enhance to 50-100. This distinctive plasticity in genome copy quantity isn't effectively understood, and continued research is required to raised understand the benefit of accumulating many chromosomes in these cells throughout stationary section.

Buchnera spp.

These micro organism are intracellular symbionts of sure aphid species. This mutualistic relationship between aphid and bacterium advanced hundreds of thousands of years ago. Though carefully related to E. coli, Buchnera has a genome approximately one-seventh the scale of the E. coli genome. In a single Buchnera species, the genome is composed of one 640 kilobase (Kb) chromosome and two plasmids, which encode the biosynthetic pathways for a number of amino acids. It has been proven that the number of genome copies in Buchnera cells is said to the developmental stage of their host aphid; as an aphid enters into adulthood, the genomic copy number in particular person Buchnera cells will increase. Because the aphid host ages, the genomic copy number in Buchnera decreases. It has been proposed that this fluctuation in copy quantity could also be because of the bacterium purging itself of genomes with deleterious mutations, guaranteeing solely viable chromosomes are transmitted to the following generation of aphids.

Agrobacterium tumefaciens

These ubiquitous, gram-unfavourable, motile, rod-formed soil micro organism are the causative agent of crown-gall illness in plants. Agrobacterium tumefaciens is known as a pure genetic engineer, as it is able to transferring DNA from itself into plant cells. The roughly 5.7 megabase (Mb) genome is comprised of a circular chromosome, a linear chromosome and two plasmids. One of many plasmids, referred to because the Ti plasmid for Tumor Inducing plasmid, is chargeable for A. tumefaciens virulence.

Epulopiscium spp.

Epulopiscium spp. are intestinal symbionts of sure species of surgeonfish belonging to the household Acanthuridae. Some morphotypes of Epulopiscium can attain lengths higher than 0.5 mm! This picture is of DAPI stained Epulopiscium cells. DAPI is a DNA-particular stain, and the entire blue that you see in these cells is definitely DNA. Assays utilizing real-time quantitative PCR counsel that Epulopiscium comprises tens of thousands of copies of its genome. This copy quantity is unprecedented in bacteria and may signify a cellular adaptation which permits Epulopiscium to keep up such a large cell measurement. By having thousands of copies of its genome, Epulopiscium could possibly synthesize macromolecules near the place they're needed in the cell, overcoming the constraints imposed by the diffusion coefficients of small molecules and biomolecules.