Cultural, Physiological, and Biochemical Identification of Actinobacteria

The traditional phenotypic tests are commonly used in actinobacterial identifica‐ tion. They constitute the basis for the formal description of taxa, from species and subspecies up to genus and family. The classical phenotypic characteristics of acti‐ nobacteria comprise morphological, physiological, and biochemical features. The morphology of actinobacteria includes both cellular and colonial characters. The physiological and biochemical features include data on growth at different tempera‐ tures, pH values, salt concentrations, or atmospheric conditions, and data on growth in the presence of various substances such as antimicrobial agents, the pres‐ ence or activity of various enzymes, and with respect to metabolization of com‐ pounds. The phenotype is the observable expression of the genotype. Gene expression is directly related to the environmental conditions. Actinobacterial phe‐ notype cannot be based on the simple observation of the organism. Strains of the most closely related taxa should be compared in their phenotypic analysis using identical methods. The comparisons must include the type strain of the type species of the appropriate genera. Furthermore, with the development of technology, mi‐ crobial physiological and biochemical identification technology is becoming fast, simple, and automated.