Bovine Mycoplasmas: Genome Size and Base Composition of DNA

Abstract

Within the order Mycoplasmatales guanine plus cytosine contents and genome sizes have been determined for 17 strains representing 15 bovine and two ovine species, subspecies or serogroups. The guanine plus cytosine contents were found to vary between 24-4 and 32.9 %. The genome sizes were 4.0 to 5-6 x 1oS daltons for 14 sterol-requiring strains and 0.99 to 1.1 x 109 daltons for three non-sterol-requiring strains. These results support earlier findings that members of the genus Acholeplasma (family Acholeplasmataceae) have genome sizes about twice those of the genus Mycoplasma (family Mycoplasmataceae). The purpose of this work was to determine the GC contents and the genome sizes of type or reference strains of all known mycoplasma species, subspecies and serogroups of bovine source. The type strains (PG2 and PG3) of two ovine organisms (Mycoplasma agalactiae subsp. agalactiae and M. mycoides subsp. Capri) were included in the study because of serological relatedness to the bovine strains ( M . agalactiae subsp. bovis (Donetta) and M . mycoides subsp. mycoides (PGI), respectively). METHODSThe mycoplasmas investigated (Table I) The substrates used for cultivation were in most cases Bacto Heart Infusion Broth (Difco), supplemented with 15 % horse serum or I % PPLO Serum Fraction, 8 % fresh yeast extract, 0.003 % phenol red, 0.08 % thallium acetate and penicillin (400 i.u./ml). Some strains were also supplied with 0.8 % glucose (PG49, PG50, B107PA7 PGI, PG3) or I % arginine (B139P7 B I~~P , ~230). Mycoplasma dispar was cultivated in FF I1 medium (Friis, 1972), with minor modifications; it comprised Bacto Brain Heart Infusion Broth (Difco, Detroit, Michigan, U.S.A.),

Determination of microbial genome sizes by two-dimensional denaturing gradient gel electrophoresis

“…The 1646 kb genome size for A. laidlawii is within the range of 1483-1703 kb measured for a number of A. laidlawii strains, by renaturation kinetics (10,13), and close to the value of 1719 determined for this strain by two-dimensional conventional gel electrophoresis (2). The 598 Hindm sites found in the A. laidlawii genome is close to the 520 sites expected assuming a random distribution of bases.…”

“…The 724 kb genome size for M. capricolum is close to the value of 758 kb, based on renaturation kinetics measurements, for M. mycoides (10), a species phylogenetically close to M. capricolum (11). The genome sizes of other Mycoplasma species are in the range of 606-803 kb, as determined by renaturation kinetics, electron microscopy, construction of an ordered clone library, and two-dimensional field-inversion gel electrophoresis (10,(12)(13)(14)(15). The 346 HindIl sites found in the M. capricolum genome is greater than the 218 sites expected based on a random distribution of bases, showing that (although the sites are randomly distributed in the genome) the number of sites cannot be approximated by a random distribution of bases in a genome with such a low G+C content.…”

The mycoplasmas.

“…Based on genome size, the mycoplasmas form two clusters: the Mycoplasma and Ureaplasma species, with a genome size of about 5 x 108 daltons, and the Acholeplasma, Spiroplasma, and Thermoplasma species, with a genome size of about 1 x 109 daltons (Table 1). As the smallest known genome size of wallcovered bacteria is around 1 x 109 daltons, the Mycoplasma and Ureaplasma species have the smallest genome recorded for any self-reproducing procaryote (8,209).…”

Pulse-field electrophoresis indicates full-length mycoplasma chromosomes range widely in size

“…1000 megadaltons) (Acholeplasma, Spiroplasma, Anaeroplasma and Asteroplasma species) and the second composed of chromosomes that cluster around 760 kbp (ca. 500 megadaltons) (Mycoplasma and Ureaplasma species) or approximately half the size of those in the first group [9][10][11][12][13].…”

“…Although chromosome sizes have been estimated for more than 30 mollicutes (representing nearly one-third of the cultivated species), no intermediate size mollicute chromosomes had been reported until recently [14]. Mollicute chromosome sizes have been estimated mainly by DNA thermal renaturation kinetics; for a few species, electron microscopy, analysis of an ordered clone library, or gel electrophoresis has been used to estimate size [9][10][11][12][13][14][15][16][17][18]. Concern has been expressed about the effect of the low G+C content of mollicute DNA on renaturation kinetic and pulsed-field gel electrophoretic determinations of chromosome size [1,19,20].…”