Genetic distance: a simple quantitative measure of biological relatedness

Molecular relatedness of Staphylococcus aureus typing phages measured by DNA hybridization and by high resolution thermal denaturation analysis

Fifteen bacteriophages representative of the serological and lytic groups of the International Typing Set for Staphylococcus aureus were examined for genomic homology by DNA hybridization and by analysis of high resolution thermal denaturation profiles. Phages 11 and 80 alpha, not part of the set, were also examined. DNA homology measured by filter hybridization showed values ranging from near zero to 88 per cent in pair-wise comparisons. Cluster analysis of these data by standard numerical taxonomical methods yielded clusters which closely reflect the subdivision of the international set on the basis of serological reactions. High resolution thermal denaturation analysis yielded characteristic profiles for each phage DNA, with members closely related by hybridization analysis showing only minor differences. Quantitative analysis of the extent of overlap of these profiles generated relational values which were subjected to the same numerical taxonomic analysis as for the DNA hybridization data. The resultant dendrogram was qualitatively different only in minor respects from that derived from the hybridization analyses, but quantitatively homology was greater by 80 per cent or more for the DNAs which were least related according to the hybridization analyses. This upward shift in measured homology appears to reflect the similar base composition of the DNAs from these phages. Statistical comparison of the homology data obtained by the two methods showed them to be significantly correlated. These results indicate that the International Typing Set consists of phages which all appear to be related to a greater or lesser extent. If, as the history of the collection of these phages indicates, they are a random sample of aureophages, then this group of phages may represent a common genetic pool within which recombination, mutation, and genome rearrangement occur to generate unique individual phages.

Genetic distance in fungus genus Fusarium measured by comparative computer analysis of DNA thermal denaturation profiles

High resolution thermal denaturation profiles of different members of fungus genus Fusarium were compared with respect to the shape of their DNA melting curves. Quantitative comparison of the shape (areas under differential curves) of all thermal denaturation profiles was made. Thermal denaturation profiles can be used to derive the quantitative parameter, genetic distance, defined by Soumpasis (12). Based on such data of genetic distance a dendrogram and a genetic distance tree was constructed.

Dual-mode computer processing for high resolution DNA thermal denaturation experiments

Two modes of data processing are appropriate in conducting high resolution thermal denaturation experiments (thermal increments of 0.05 degrees or closer). In the first mode, a general purpose microcomputer provides on-line services important to the control and monitoring of the initial experiment, including control of the spectrophotometer and heater, the recording of data, and the display of current hyperchromicities and approximate first derivatives. A subsequent microcomputer program then reads the recorded data files and carries out accurate calculations of derivative denaturation profiles and the estimate of the statistical error of the first derivative at each point. The data collection program handles three samples at a time and was designed to provide optimal results in thermal denaturation experiments with a single-beam spectrophotometer.

Similarity of genetic distance determined from DNA thermal denaturation profiles to standard estimates of bacteriophage relatedness

High resolution thermal denaturation profiles of a series of potentially related bacteriophages of Bacillus subtilis contain a multitude of distinctive features that permit them to be divided into at least four groups. In addition, the profiles can be used to derive the quantitative parameter, genetic distance, defined by Soumpasis (Soumpasis, D. (1980) J. Theor. Biol. 86, 137-147). Both the quantitative and the qualitative intercomparisons of profiles are in general agreement with the results of standard techniques for estimating genetic relatedness.