Biological, Biochemical and Biomedical Aspects of Actinomycetes - Part B [antikvár]

Introduction Actinomycetes constitute a group of microorganisms within the Procaryotic Kingdom which shows many similarities with microscopic fungi, with which they are a classical example of convergent evolution. Specially relevant in this context are the morphology and mycelial organization of their colonies as well as their systems of reproduction. One may speculate that these similarities arise from a common adaptation to fulfill their metabolic functions in the absence of water in their immediate environment. The life cycle of streptomyceteis growing on solid media involves the formation of two different types of mycelia: firstly, a substrate mycelium that grows on and into the culture medium and, as the colony matures, a second type of mycelium which grows into the air and will finally form the spores. During colony growth, aerial hyphae develop in absence of water and, because of this, must be protected from dehydration. On the other hand, and due to the previous growth of the substrate mycelium, aerial hyphae develop under unfavourable conditions such as the exhaustion of nutrients and accumulation of inhibitory compounds in the culture medium. Changes in colony organization of Streptomyces during the develop- mental cycle were studied by Wildermuth (1970). However, very little information is available about the physiological events that occur during aerial mycelium growth and sporogenesis. This may, in part, be due to the technical difficulties imposed by the fact that these differentiation processes take place only on solid media. It must be kept in mind that, as Kalakoutskii and Agre (1976) suggested, the physiological and biochemical data obtained with submerged shaken cultures must be taken with considerable caution when interpreting morphogenetic changes observable in surface cultures. The cellophane transfer technique is a useful tool to achieve a better understanding of the physiological and biochemical events that take place during the different stages of the streptomycetes life