Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 1: INTRODUCTIONtime effective manner (Siegal et al., 1999). A novel approach used for the discoveryof biologically active microbial secondary metabolites from both crude or pureextracts is known as biomolecular-chemical screening. This method combines TLCand reactivity of metabolites using various staining reagents with binding tobiomolecules like DNA (Maier et al., 1999).Table 2. Variation of culture conditions (adapted from Zähner & Fiedler, 1995)Nutrient broth• use of nutrient broth which prevents carbon, nitrogen and phosphorus repression, ifpossible• use of nutrient broths with an excess of carbon and limited nitrogen supply andvice versa• medium supplementing towards the end of growth phase • nutrient broth deficientin trace elementsPhysical conditions• temperature, possible shift in temperature towards end of log phase• pH including pH shift during culture • pO 2 • pCO 2 • osmotic valuesCollection of metabolites using adsorber resin• or ion exchanger during fermentation or removal of metabolites by dialysis,for example using a membrane fermenterCreation of stress conditions• osmotic stress • stress through heavy metals • stress through inhibitorsupplementMicrobial conversions of certain parent substances• incorporation of modified modules using deliberate fermentation• incorporation of modified modules using mutasynthesis• microbial transformation of biologically active parent substances_____________________________________________________________________10