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Agreement between deoxyribonucleic acid base composition and taxometric classification of grampositive 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.

The mechanism of action of rifampicin, an antibiotic which inhibits in vitro the polycondensation of ribonucleotides by ribonucleic acid (RNA) nucleotidyltransferase, was studied in vivo in Escherichia coli . It is argued that the inhibition of RNA nucleotidyltransferase represents the primary lesion and is responsible for the bactericidal effect. This conclusion is based on (i) the correlation between concentrations of the antibiotic which block in vivo incorporation of labeled uracil and the bactericidal concentrations, (ii) the evidence that the loss of viability of the cells immediately follows the block of RNA synthesis, and (iii) the observation that the reversal of the inhibition of RNA synthesis goes together with a reversal of the loss of viability.

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