Genetic structure of populations of beta-haemolytic Lancefield group C streptococci from horses and their association with disease.

The genetic structure of beta-haemolytic Lancefield group C streptococci isolated from horses in Australia was examined by multilocus enzyme electrophoresis. The 249 isolates comprised 70 classified phenotypically as Streptococcus equi subspecies equi, 177 classified as S equi subspecies zooepidemicus and two which were unclassifiable. Forty-one electrophoretic types were identified which could be classified into three major clusters, A, B and C. Of the isolates, 178 fell into cluster B (types 4 to 22) and lay within a genetic distance of 0.36. Sixty-nine of the 70 S equi subspecies equi isolates fell into type 12, which suggests that they were members of a single clone, and the isolates from abscesses were significantly more likely to belong to type 12 than those from horses with no clinical signs (P < 0.001). There were no other significant associations between electrophoretic types or clusters and the isolation of the organism from particular sites. These data suggested that S zooepidemicus may be the archetypal species from which the clone designated subspecies equi has been derived. If isolates of the subspecies equi from other geographical regions also prove to be members of electrophoretic type 12, this hypothesis would be strengthened.

Genetic Diversity in Cellular Slime Molds: Allozyme Electrophoresis and a Monoclonal Antibody Reveal Cryptic Species among Dictyostelium discoideum Strains.

Cellular slime molds have been classified on the basis of a small number of descriptive criteria such as fruiting body color and morphology, and, in heterothallic species, by assignment to compatible mating groups. However, some isolates which are morphologically classified as conspecific do not fall into a simple mating-type classification; for example some are asexual or homothallic. An increasing interest in inter-strain genetic variation in studies of development and simple behavior has led us to reassess genetic relationships among a number of frequently used isolates. Allozyme electrophoresis of 16 soluble enzymes and use of a monoclonal antibody show that there is relatively little genetic diversity among sexually competent Dictyostelium discoideum isolates, despite considerable variation in geographic origin and time since isolation in the laboratory. In contrast a pair of asexual strains and each of two homothallic strains are genetically quite distinct and differ sufficiently from each other, and from sexually competent isolates, to warrant their recognition as separate species. There are probably four biological species represented in the supposedly D. discoideum isolates studied. This heterogeneity extends to other cellular slime mold species. Each of three isolates of Dictyostelium purpureum is genetically distinct from the others. Limited analysis of other cellular slime molds indicates that the generic distinction of Dictyostelium and Polysphondylium must be questioned. This study emphasizes that caution should be applied in classifying simple organisms on morphological criteria.

Karyotypes, constitutive heterochromatin and taxonomy of ringtail opossums of the genus Pseudocheirus (Marsupialia: Petauridae).

Karyotypes are presented for three forms of the common ringtail oppossum, Pseudocheirus peregrinus. These are tentatively regarded as the subspecies P.p. cookii, P.p. pulcher, and P.p. rubidus. In addition, we report for the first time the karyotype of the rock ringtail oppossum, P. dahli. The three forms of P. peregrinus each have a diploid number of 2n=20. C-banding studies indicate that the addition of large blocks of constitutive heterochromatin has played a major role in the evolution of all chromosomes in the karyotype. The X chromosome of P.p. pulcher is metacentic and approximately twice the relative size of the acrocentric X chromosomes of the other two forms of peregrinus. All three forms had two or three pairs of autosomes with secondary constrictions, a rare occurrence within the superfamily Phalangeroidea. P. (Pseudochirops) dahli has a diploid number of 2n=16; a reduction in chromosome number may have occurred by Robertsonian fusions. Four of the eight chromosome pairs lack large blocks of C-band material and the secondary constrictions are located on the sex chromosomes.

Studies on metatherian sex chromosomes. IX. Sex chromosomes of the greater glider (Marsupialia: Petauridae).

The greater glider, currently but incorrectly known as Schoinobates volans, is widely distributed in forested regions in eastern Australia. All animals studied from six different localities had 20 autosomes but there were four chromosomally distinct populations. At Royal National Park, N.S.W., all female greater gliders studied had 22 chromosomes including two large submetacentric X chromosomes with subterminal secondary constrictions in their longer arms. This form of X chromosome occurred also at Bondo State Forest, Myall Lakes and Coff's Harbour, N.S.W., and at Eidsvold, Qld. At Coomooboolaroo, Qld, the X chromosome was also a large submetacentric but a secondary constriction occurred in the shorter arm. Two chromosomally distinct types apparently occur in Royal National Park, one with XY males as in all other populations, and one with XY1Y2 males. Y or Y1, but not Y2, chromosomes were eliminated from the bone marrow in all populations but were present in spermatogonia, primary spermatocytes and cultured fibroblasts. Animals from Bondo State Forest had three or more acrocentric or metacentric supernumerary chromosomes.