Genome size and life cycle of the mycoplasma

Department of Molecular Biophysics and Biochemistry and Department of Microbiology Yale University New Haven, Connecticut 06520
Annals of the New York Academy of Sciences (Impact Factor: 4.38). 12/2006; 225(1):62 - 73. DOI: 10.1111/j.1749-6632.1973.tb45637.x
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    • "For instance, it is likely that the larger size of intracellular parasite genomes, as compared to those of endosymbionts, is due to the presence of genetically encoded specifically related to parasitic lifestyles, such as sequences involved in host-parasite recognition and infection mechanisms. Figure 1 provides no support for the hypothesis that the size distribution of extant prokaryotic chromosomes is the outcome of a series of whole genome duplications that begun with an ancestral 800 kb minigenome as suggested by Wallace and Morowitz (1973) and Herdman (1985). Since there are no known free-living prokaryotes with genomes smaller than the 1450 kb, 1500 kb, and 1530 kb of Halomonas halmophila (Mellado et al., 1998), Aquifex pyrophilus (Shao et al., 1994) and Fervidobacterium islandicum, respectively, the extrapolation of a normal distribution curve beyond this cut-off value does not seem justified. "
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    ABSTRACT: The concept of a minimal cell is discussed from the viewpoint of comparative genomics. Analysis of published DNA content values determined for 641 different archaeal and bacterial species by pulsed field gel electrophoresis has lead to a more precise definition of the genome size ranges of free-living and host-associated organisms. DNA content is not an indicator of phylogenetic position. However, the smallest genomes in our sample do not have a random distribution in rRNA-based evolutionary trees, and are found mostly in (a) the basal branches of the tree where thermophiles are located; and (b) in late clades, such as those of Gram positive bacteria. While the smallest-known genome size for an endosymbiont is only 450 kb, no free-living prokaryote has been described to have genomes < 1450 kb. Estimates of the size of minimal gene complement can provide important insights in the primary biological functions required for a sustainable, reproducing cell nowadays and throughout evolutionary times, but definitions of the minimum cell is dependent on specific environments.
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    ABSTRACT: Serological techniques are recommended procedures for the identification of Mycoplasma species. They enable separation of mycoplasmas at the species level and are widely used for practical laboratory identification of the isolated microorganisms. However, complex growth media are required for the isolation of Mycoplasma species and some strains of pathogenic Mycoplasma species grow very fastidious and can not be cultured. Introduction of DNA based diagnostic methods in mycoplasma research enabled survey of the whole genome in a single assay and reveal also information about non- coding regions of the genome. Restriction enzyme analysis is a powerful method for differentiation of close related strains but requires high quality of DNA which can only be obtained from cultured mycoplasmas. The increasing number of cloned mycoplasma genomic fragments are successfully used for identification and differentiation of mycoplasma strains and species in hybridization studies. The polymerase chain reaction enables identification and characterization of mycoplasmas without culture directly from clinical material. Large genomic sequencing projects produced complete nucleotide sequence from two Mycoplasma species and several more are in progress. This data will open the possibility to understand better the biology of mycoplasmas.
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