Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 1: INTRODUCTIONcontrolled excess DOC throughout the SM fermentations. Oxygen limitation has beenshown to abolish SM biosynthesis in Amycolatopsis orientalis and S. clavuligerus(Dunstan et al., 2000; Ives & Bushell, 1997).1.7.2.7 Precursors, Cofactors and NucleotidesThe availability of metabolite precursor and cofactor levels influence the regulation ofsecondary metabolites (Kheton et al., 1999). As many biosynthetic enzymes have alow substrate specificity, analogues can be added as precursors and these can beincorporated to give hybrid products (Jacobsen et al., 1997; Brown et al., 1999). Anexample of precursor directed biosynthesis is that of efrotomycin by Nocardialactamdurans, the rate limiting step in the biosynthesis of this metabolite is theavalability of uracil, the precursor of the pyridone moiety of this metabolite. Thedifferent types of molecules serving as precursors have included short chain fattyacids which have been shown to enhance SM production (Ohno et al., 1980; Untrau-Taghian et al., 1995; Cruz et al., 1999), purines and nucleotides, such asnicotinamide-adenine-dinucleotide (NADH), adenosine and guanosine phosphates,pyridoxal 5’phosphate which have been implicated in the regulation of SMbiosynthesis (Gräfe et al., 1994).1.7.2.8 Enzyme Inhibitors and Repressors of SecondaryMetabolismA severe consequence of the production of secondary metabolites is the inhibition orrepression of their biosynthetic enzymes (Table 15). Other contributing factors toenzyme inhibition include certain organic acids and amino acids which when added tomedia, repress the production of specific biosynthetic enzymes (Iwai & Ōmura,1982).Table 15. Enzyme Inhibitors of Secondary Metabolite Production in Actinobacteria.Secondary Enzyme Inhibitor EnzymeReferencesMetaboliteEffectedStreptomycin Chloramphenicol Amidinotrasferase Martin and Demain, 1980Actinomycin Chloramphenicol Phenoxazione Katz and Weissbach, 1962PuromycinSynthaseChloramphenicol p-aminophenylalanine Arylamine Synthase Jones and Westlake, 1974Candicidin Rifampin CandicidinSynthetaseLiras et al., 1977_____________________________________________________________________45