The Family Streptomycetaceae, Part II: Molecular Biology
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The Family Streptomycetaceae, Part II: Molecular Biology HILDGUND SCHREMPF
Introduction Some members of the order of Actinomycetales were already identified about a century ago (for review, see Kutzner, 1981). The current phylogenetic tree includes Bifidobacteriaceae, Actinomycetaceae, Arthrobacteriaceae, Cellulomonadaceae, Microbacteriaceae, Dermathophylaceae, Propionobacteriaceae, Nocardioidaceae, Frankiaceae, Corynebacteriaceae, Mycobacteriaceae, Nocardiaceae, Actinoplanaceae, Pseudonocardiaceae, Streptomycetaceae and Streptosporangiaceae. The family Streptomycetaceae includes the genus Streptomyces, which comprises strains formerly classified as Chania, Elytrosporangium, Kitasatoa, Kitasosporia, Actinosporangium and Streptoverticillium. All members of the Streptomycetaceae family have a complex life cycle, featuring an extended vegetative substrate mycelium and aerial hyphae, in which spores form upon depletion of nutrients. They contain specific menaquinones, incorporate LLdiaminopimelic acid (a diagnostic amino acid) into their peptidoglycan, but lack a diagnostic sugar (Kutzner, 1981). In addition they contain characteristic signatures within the genes for 23S and 16S rRNA (Roller et al., 1992; Embley and Stackebrandt, 1994). An enormous number (>800) of Streptomyces species has been described by numerical taxonomy (Goodfellow et al., 1990). Kämpfer presents the current methods for classification in an another chapter, The Family Streptomycetaceae, Part I: Taxonomy, in this Volume. Sixty years ago, streptomycin was the first antibiotic which was classified from a Streptomyces strain. Since then, streptomycetes have proved to be the richest sources of thousands of lowmolecular weight, chemically different compounds having antibacterial, antifungal, antiparasitic, agro-active, cytostatic or other biological activities. Additionally, they have provided many enzymes which are required for the natural turnover of many macromolecules in soil. As outlined in this chapter, the tools of molecular biology in combination with physiological,
biochemical, and genetic studies have considerably deepened understanding of the biology of streptomycetes. This knowledge is the current and future basis for exploiting the seemingly endless repertoire of metabolites and activities of the family of Streptomycetaceae.
The Developmental Growth Cycle Growth Characteristics Streptomycetes grow by tip extension as long, branching vegetative hyphae, which rarely have septae. The compartments within the substrate hyphae contain numerous copies of the chromosomal DNA. Aerial hyphae begin to form upon depletion of nutrients. The aerial structures contain several surface layers. One of them is the hydrophobic rodlet layer, which comprises the proteins RdlA and RdlB. The corresponding genes within Streptomyces coelicolor A3(2) and S. lividans are expressed within growing aerial hyphae but not within spores (Claessen et al., 2002). Partitioning of the chromo
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