Deoxyribonucleic acid base composition of species ofKlebsiella,Azotobacter andBacillus

Methods of molecular taxonomy were used to study the genome or deoxyribonucleic acid (DNA) of different strains of five genera of nitrogen-fixing bacteria. The DNA base compositions of all strains ofKlebsiella pneumoniae (previously classified as strains ofAchromobacter sp.,Aerobacter aerogenes orK. pneumoniae) occupy a fairly narrow range of values from 56.7 to 62.5% G-C content. No significant difference was observed in the DNA base composition of bacteria which can fix molecular nitrogen and that of strains which do not fix nitrogen.Six strains of the speciesAzotobacter vinelandii and the one strain ofA. chroococcum tested possess similar DNA base composition. The strain ofAzotobacter agilis tested, however, had a DNA base composition different from these seven strains. The G-C content of the strains ofAzotomonas insolita falls within the broad range of thePseudomonas genus (55–70%), but the peritrichous flagellation of these strains eliminates them from this genus. Their classification still remains to be ascertained.Eleven strains of the speciesBacillus polymyxa andB. macerans formed two homogenous groups of organisms with different DNA base composition. The atypical strainB. polymyxa Hino is genetically similar to the strains of the speciesBacillus macerans and perhaps should be reclassified as such.Supported in part by National Science Foundation grant GB-483 and National Institutes of Health grants AI 01417 (11) and based on Ph.D. thesis of senior author (1967).     

DNA base composition of yellowErwinia strains

DNA base composition, expressed as % GC, was determined in 34 strains of yellow-pigmentedErwinia-like organisms from plant, animal and human origin. Organisms calledErwinia herbicola (Graham and Hodgkiss, 1967) have a % GC in the narrow range 55.0 to 56.5, with the exception of strain G 146 which has 58.6% GC. They include the formerBacterium herbicola, Erwinia lathyri, Bacterium typhi flavum and the Muraschi isolates,Erwinia milletiae with 55.8 % falls within the % GC range of theHerbicola group,Erwinia ananas is at the lower end of the group with 54.8 ± 0.4 % GC andErwinia uredovora still lower at 53.7 ± 0.7 % GC. These data and the compositional distribution of the DNA fragments do not exclude the inclusion of these organisms into the genusErwinia.     

DNA base composition of extremely halophilic cocci

Summary The percentage guanine+cytosine (GC) content of the DNA of 9 extremely halophilic cocci were determined from melting temperature (T _m) and the E ₂₆₀/E ₂₈₀ ratio at pH 3. The values found ranged from 60.5–65.8, with an average 62.6% GC.     

DNA base composition of some sheathed bacteria

The DNA base composition of five recently isolated Haliscomenobacter hydrossis strains were compared with those of Sphaerotilus natans, Leptothrix cholodnii and Leptothrix discophora. The DNA base composition of H. hydrossis strains ranged from 48.3 to 49.7% GC, whereas the % GC values of S. natans, L. cholodnii and L. discophora were found to be 69.7, 69.6 and 71.2, respectively. These results indicate that Haliscomenobacter species and the microorganisms of the Sphaerotilus-Leptothrix group should not be classified into the same genus, as they are genetically at best remotely related.The reallocation of some Leptothrix species into the genus Sphaerotilus is not in contradiction with their DNA base composition.     

Spectrofluorometric determination of bacterial DNA base composition

A spectrofluorometric technique for bacterial DNA base composition has been developed. This fast and simple technique requires two fluorescent dyes and a few inexpensive reagents. The data from this assay indicate that the guanine-cytosine content obtained was within acceptable statistical limits in comparison to commonly cited literature values. The spectrofluorometric technique is reliable and reproducible.     

DNA base composition of species of the genusSaccharomyces

DNA base compositions (GC content) ofSaccharomyces species are reported and discussed. Several amendments of the four groups given by van der Walt are suggested, viz. the transfer ofS. kluyveri to group 1, and ofS. eupagycus, S. cidri, S. montanus, S. microellipsodes andS. florentinus to group 2. The synonomy ofS. amurcae andS. cidri is suggested. The DNA base compositions revealed two possible pairs of sibling species:S. elegans andS. bailii, with a difference in GC content of 4.1%;S. dairensis andS. servazzii with a difference in GC content of ca. 3%.S. mrakii had a GC content of 47.3–48.5% the highest encountered in this genus and similar to that ofKluyveromyces thermotolerans.     

DNA base composition and taxonomy of someAcinetobacter strains

The DNA base composition of a group of numerically analyzed acinetobacters was determined. Seven strains ofAcinetobacter anitratus appear to form a homogeneous group with S>90% and ca. 42.1 % GC.A. Iwoffii is less homogeneous. Most of the strains have around 46.6 % GC and a broad compositional distribution with 2=3.8 C. Two other small groups have a % GC of 44.8±0.3 and 42.1±1 % GC. The DNA characteristics of the latter group are indistinguishable fromA. anitratus-DNA. ThreeAlcaligenes faecalis strains have 58.8 % GC. Numerical analysis suggests that they might be related toBordetella bronchiseptica, but the % GC of the latter (69.5) shows that the relationship is only remote.     

Intramolecular base composition heterogeneity of human DNA.

The intramolecular base composition heterogeneity of human DNA has been investigated by electron microscopic observations of partially denatured structures and by equilibrium solution thermal denaturation techniques. DNA sequences having an average length of less than 2000 base pairs are found to be heterogeneous in base composition. These heterogeneous sequences occupy a minimum of 67 to 81% of the human genome.     

DNA base composition and adansonian analysis of mycobacteria

The contents of guanine and cytosine (GC) in DNA were determined in 20 strains of rapidly growing mycobacteria, 18 of which were originally classified as 8 different species and 2 were not defined. The values of GC expressed in molar percentage varied between 63.3 and 67.9 and agreed generally, as well as individually in the various species, with data reported in the literature for the genusMycobacterium (60.8–73.0% GC). In addition to the determination of GC in DNA, 20 mycobacteria were tested for various physiological and biochemical characteristics (a total of 82 characters were processed). Adansonian analysis was applied to establish similarity between individual pairs of microorganisms as to their phenotypic expression. All the mycobacteria used were divided into 6 groups (group 2 was subdivided into 3 sub-groups) of phylogenetically related organisms with a high percentage of similarity (S≤70%) and with great similarity in the GC content in DNA (±1% GC).     

Taxonomy ofKluyveromyces: evaluation of DNA base composition

The DNA base composition of 19 strains ofKluyveromyces was calculated from the thermal denaturation temperature (Tm) of their DNA. The % GC ranged from 33 to 45, with a bimodal repartition. It may be inferred that the intrageneric variation is too weak to discriminate two genera. However, two groups can be distinguished on the base of % GC and two other criteria of classification. associated with the Centre National de la Recherche Scientifique. The authors are indebted to Professor Dr. J. De Ley for his advice on the thermal-denaturation technique and to Mrs. Billon-Grand for her skilful technical assistance.     

DNA base composition and DNA relatedness among species of Trichosporon Behrend

The nuclear DNa of 28 species (30 strains investigated) of yeasts classified currently or previously in the genus Trichosporon. was analysed for its molar percentage of guanine + cytosine (mol% G+C). This criterion, together with biochemical characteristics, suggested the separation of the organisms studied into two groups. The first group, which appears related to the Ascomycetes, includes thirteen species with a G+C content lower than 50 mol% (34.7–48.8), and lacks urease (except T. margaritiferum). The second group appears related to the Basidiomycetes and includes fifteen species with a G+C content higher than 50 mol% (57–64) and has the ability to hydrolyse urea.A DNA homology experiment with T. beigelii and twelve other species of the second group showed very low values of complementarity with T. beigelii-labeled DNA. All these species must be considered as taxa other than T. beigelii.     

Relationship between base composition in non-coding DNA of genes and codon composition

The C + G percentage in third position of codons is linearly dependent on the C + G composition of flanking regions and introns. A similar relationship is shown for the first and second position which significantly influence the nature of amino acid sequence. If mutations would be oriented according to the local base composition, this will imply that genes of the same multigenic family would evolve at different rate.     

The relationship of DNA base composition and individual protein composition in micro-organisms

Summary To investigate the dependence of protein composition on DNA base composition, a set of data on individual proteins with known amino acid compositions from a spectrum of bacterial species has been compiled. It is found that similar relationships of amino acid frequency to G + C content exist for these proteins as for the bulk proteins studied by Sueoka (1961). The data are analysed by linear and cubic regression, and a measure of the proportions of A + T-rich and G + C-rich codons in the underlying messenger RNAs is put forward. The theoretical limits on the G + C content of coding DNA are discussed, and inference are made about the various selective forces acting on DNAs of different G + C contents.