Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 1: INTRODUCTIONuses (Kurtböke, 2000). An innovative approach makes use of current moleculartechniques to rationally design hybrid molecules by genetically modifyingbiosynthetic genes, to achieve specific biological functions (Khosla, 1998).Additionally, actinobacteria are important sources of novel genes encoding enzymeswhich are involved in catalytic reactions forming complex structures such as the tripleintramolecular carbon-carbon bonds seen in the molecular structures of theinsecticidal compounds of the spinosyns rarely seen in other macrolide compounds(Waldron et al., 2001).1.1.3 Sources of Actinobacteria Secondary Metabolite DiversitySecondary metabolites, also known as idiolites, are microbial compounds oftenpossessing complex chemical structures, which result from long enzymatic pathways.They are produced under specific conditions, usually after the growth phase hasended, in submerged culture. Secondary metabolites are produced by restrictedtaxonomic groups of organisms and are usually formed as mixtures of closely relatedmembers of a chemical family.Phenomenal biochemical pathways produced by diverse actinobacteria isolated fromunique natural environments, have been shown to produce bioactive compoundswhich exert their influence by processes that are not compromised by existing multidrugresistance pathways (Capon, 1998). Some actinobacteria are more prevalent orsuited to particular environments than others (Jiang & Xu, 1993; Kurtböke &Wildman, 1998). Terrestrial habitats have been the major source of SM producingmicroorganisms. However, marine habitats are providing an alternative sourceyielding a diverse range of metabolites exhibiting novel structures (Jensen & Fenical,1994). A number of key genera are adapted to symbiotic commensalism and extremeenvironments and these groups have received little attention because they are difficultto isolate and culture (Strobel & Long, 1998). In addition, Jiang & Xu (1993) showedthat a great deal of actinobacterial diversity exists in extreme environments. Byunderstanding the ecological roles of rare actinobacteria, isolation procedures will bebetter suited to cultivating these rarer or novel genera thus enhancing microbialdiversity (Suzuki et al., 1994)._____________________________________________________________________2