Agreement Between Deoxyribonucleic Acid Base Composition and Taxometric Classification of Gram-Positive Cocci.

Silvestri, L. G. (Università Statale, Milan, Italy), and L. R. Hill. Agreement between deoxyribonucleic acid base composition and taxometric classification of gram-positive cocci. J. Bacteriol. 90:136-140. 1965.-It had been previously proposed, from taxometric analyses, that gram-positive, catalase-positive cocci be divided into two subgroups. Thirteen strains, representative of both subgroups, were examined for deoxyribonucleic acid (DNA) base composition, determined from melting temperatures. Per cent GC (guanine + cytosine/total bases) values fell into two groups: 30.8 to 36.5% GC and 69 to 75% GC. Strains with low per cent GC values belonged to the Staphylococcus aureus-S. saprophyticus-S. lactis taxometric subgroups, and those with high per cent GC values belonged to the S. roseus-S. afermentans subgroup. The hypothetical nature of any classification is emphasized, and, in the present work, the hypothesis derived from taxometric analyses of division into two subgroups is confirmed by the study of DNA base ratios. The two subgroups correspond, respectively, to the genera Staphylococcus and Micrococcus.     

Effect of dark repair on ultraviolet sensitivity of bacteriophage-infected bacteria

Feiner, R. R. (Columbia University, New York, N.Y.), and R. F. Hill. Effect of dark repair on ultraviolet sensitivity of bacteriophage-infected bacteria. J. Bacteriol. 91:1239-1247. 1966.-Changes in ultraviolet (UV) sensitivity of phage-host complexes during phage development have been studied for the following systems: T1 and Escherichia coli B, T1 and E. coli K-12S, lambda and E. coli K-12S. Complexes were formed with bacterial strains differing in ability to dark-repair UV damage to deoxyribonucleic acid and, after irradiation, were plated on bacteria differing similarly. In the first half of the latent period, the resistance of complexes formed with nonrepairing bacteria increased considerably; with T1 and E. coli B hcr(-), in 4 min the resistance became the same as that of complexes formed with repairing bacteria. The repair ability of plating bacteria affected survival curves only upon irradiation in the second half of the latent period after mature phages were present in the initial complex. Use of nonrepairing bacteria both for initial infection and for plating of late complexes resulted in a series of survival curves showing for all three systems the same pattern of change originally reported for T2-E. coli B complexes. Thus, a hitherto unexplained difference between radiation survival curves for T-even and T-odd phages seems due to repair of T-odd phages by the host.     

Computerized matching of relevés and association tables,with an application to the British National Vegetation Classification

When a new relevé is to be assigned to a pre-existing type, its composition is compared with an association table. Bayesian inference may seem a good way to make the comparison, but presents difficulties. In an alternative approach, three indices of goodness-of-fit are proposed. Compositional satisfaction is a measure of how well the species composition of the relevé fits the constancy classes in the table; it is a minor modification of the Czekanowski coefficient of similarity between observed and expected numbers of species in each constancy class. Dominance satisfaction is a modification of the Czekanowski similarity between the relevé and cover values that might be expected from the association table. Dominance constancy is a weighted mean of the constancy class of the four most abundant species in the relevé. A computer program, TABLEFIT, combines them into a single index. It has been tested on British mire vegetation.     

Supplemental oxygen reduces right ventricular hypertrophy in monocrotaline-injected rats

We evaluated the possible contributory role of hypoxia in the development of monocrotaline-induced pulmonary hypertension. Male Sprague-Dawley rats were injected subcutaneously with monocrotaline (60 mg/kg) or saline in controls and were kept in oxygen-enriched (inspired O2 fraction of 0.35) or compressed air chambers. After 21 days, rats were anesthetized while spontaneously breathing room air, hemodynamic parameters and arterial blood gases were measured, and animals were killed. Right ventricular peak systolic pressures (RVPP), right ventricular-to-left ventricular plus septal weight ratios (RV/LV + S), hematocrits, lung dry weight-to-body weight ratios, and medial thickness of pulmonary arteries were significantly reduced in monocrotaline-injected rats exposed to mild hyperoxia compared with air. The air-exposed monocrotaline-injected rats had significantly more arterial hypoxemia than the other groups, and mild hyperoxia had no effect on any of the measured variables in saline-injected rats. To determine whether the effects of mild hyperoxia occurred early or late after monocrotaline injection, we moved separate groups of rats from air to mild hyperoxia and vice versa 10 days after monocrotaline injection. After 21 days, significant reductions in RVPP and RV/LV + S occurred only in rats exposed to mild hyperoxia during the latter 11 days after injection. Our findings suggest that hypoxia contributes to the development of pulmonary hypertension relatively late after monocrotaline injection in rats but that it does not influence the early injury.     

Sewall Wright and quantitative genetics

Some aspects of Wright's great contribution to quantitative genetics and animal breeding are reviewed in relation to current research and practice. Particular aspects discussed are as follows: the utility of his definition of inbreeding coefficient in terms of the correlation of uniting gametes; the maintenance of genetic variation in the optimum model; the inter-relations between past and present animal-breeding practice and the shifting-balance theory of evolution.