Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 1: INTRODUCTIONSection 2: Biology of Secondary Metabolism and theDiscovery of Secondary Metabolites in Actinobacteria1.2.1 Microbial Secondary Metabolism1.2.1.1 Secondary Metabolite ProductionMicrobial derived secondary metabolites can be metabolic intermediates or endproducts from intricate and often lengthy biosynthetic pathways. Secondarymetabolites may be found in various species in disparate genera or families and avariety of metabolites can be expressed from a single species under differentenvironmental conditions. Secondary metabolites are derived from the precursors andenergy generated through primary metabolic pathways (Figure 1). The SM groupscommonly distributed in nature are the polyketides, terpenes, steroids, shikimic acidand alkaloids (Herbert, 1989). The diversity of structures generated are a result ofmodifications and combinations of reactions from primary metabolic pathways. Mostsecondary metabolites are low molecular weight compounds having molecular massesless than 1500 Daltons.Figure 1. Primary metabolic pathways leading to the formation of secondarymetabolites (adapted from August et al., 1999).The biosynthesis of secondary metabolites in actinobacteria involves the followingsequence of events; 1) uptake of nutrients into the cell and conversionintointermediates of primary metabolism, 2) accumulation of primary metabolites andsignalling molecules induces secondary metabolite production, 3) primary_____________________________________________________________________5