Genetic, morphological and physiological relationships among coryneform bacteria

The DNA base composition of the soil arthrobacters tested (65.3 - 67.0% GC) suggests that this group is genetically homogeneous. Hybridization experiments, however, revealed clear differences between the Arthrobacter simplex and the Arthrobacter globiformis strains. The orange cheese coryneforms were fairly homologous, which was shown by the narrow %GC range (63.2 - 63.8, except one strain), the significant hybridization with the type species Brevibacterium linens, and the mutual morphological and physiological resemblance. The majority of the orange sea-fish coryneforms  resembled both morphologically and in their GC contents the Brevibacterium linens group; the results of hybridization experiments and physiological studies indicated, however, that only a minority of the sea-fish strains are closely related to the orange cheese coryneforms. With the exception of four strains tested, the majority of the non-orange cheese strains were closely related as concluded from their GC contents (65.5 - 66.9%) and their high degree of hybridization. The soil arthrobacters, the orange cheese and sea-fish coryneforms, and the non-orange cheese coryneforms were found to be only
remotely related because of the poor hybridization between the DNAs of the respective reference strains in addition to differences in GC contents or morphological and physiological characters, or both. In general, the results obtained from DNA analysis and DNA-DNA hybridization experiments and those from morphological and physiological studies were found to be fairly well correlated. A comparative study with native and deep-frozen DNA revealed that freezing at -70 °C and subsequent storing at -21°C for at least half a year had no significant effect on thermal denaturation and hybridization. In the initial renaturation phase, mismatching in hybrids of closely related DNAs was restricted to a few %, and in those of moderately related DNAs to approximately 10%.