Determination of DNA base compositions from melting profiles in dilute buffers

Identification and characterization of Moraxella phenylpyruvica

Eight strains of Moraxella phenylpyruvica have been isolated from clinical material in the United Kingdom, the first to be reported from this country. They were characterized, together with three strains of M. phenylpyruvica of the National Collection of Type Cultures (NCTC), and compared with NCTC strains of eight other Moraxella species. The strains of M. phenylpyruvica formed a homogeneous group which is readily distinguishable from other Moraxella species. Deamination of phenylalanine is not restricted to M. phenylpyruvica which, however, is urease positive and is stimulated by bile, in contrast to other Moraxella spp.

Transferable drug resistance in Pseudomonas aeruginosa

Three strains of Pseudomonas aeruginosa were demonstrated to transfer double-drug resistance by conjugation to a P. aeruginosa recipient at frequencies of 10(-4) to 10(-2) per recipient cell. Two of the three strains also transferred to Escherichia coli at frequencies which were 10(3)- to 10(5)-fold lower, but the third strain could not be demonstrated to do so. The latter strain, however, conferred maleness on the Pseudomonas recipient. The transfer of streptomycin resistance was associated with the acquisition of streptomycin phosphorylase by both P. aeruginosa and E. coli recipients. Maximal broth mating frequencies were obtained with nonagitated cultures less than 1 mm in depth. A pyocine selection system based on donor sensitivity and recipient resistance is described and appears to have future value as a generalized selective device for use after matings.

Correlation of melting temperature and cesium chloride buoyant density of bacterial deoxyribonucleic acid

Samples of bacterial deoxyribonucleic acid from bacteria having guanine plus cytosine (GC) contents in the range of 27 to 72 moles per cent GC were analyzed by optical melting (T(m)) and equilibrium buoyant density methods. The relation between these properties is shown to be linear. The relative value of 1.99 moles per cent GC per degree C change in T(m) is calculated, and a reference method for the calculation of GC contents relative to a standard is derived.