Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 1: INTRODUCTIONantibiotic producing strains S. griseocarneus and S. natalensis the use of sporeinoculums showed an increase in polyene yields as compared to the use of vegetativecells, additionally spore concentrations of 2 x 10 7 - 10 8 spores/ml were found to beoptimal (Cruz et al., 2000; El-Enshasy, 2000). Conversely, late exponential growthphase mycelia was used as the inoculum source for the beta-lactam producing strainS. clavuligerus, which caused a increase in the production of clavulanic acid andshortened the duration of the fermentation (Neves et al., 2001).The use of controlled-release polymers such as ethylene-vinylacetate containingammonium chloride (NH 4 Cl) has been used to efficiently release NH + 4 to S.clavuligerus and avoiding the repressing effects of high NH + 4 and evidently leadingto a increase the production of cephalosporin (Lübbe et al., 1985).1.7.3 Solid State FermentationsAlternative fermentation systems such as solid state fermentations (SSF) are beingadapted to the production of secondary metabolites (Robinson et al., 2001). SSF ischaracterised by containing the following properties (1) a fermentation processoccurring on solid porous matrices which can either be natural materials (such as rice,wheat bran) or an inert support (e.g. polystyrene, vermiculite) impregnated with aliquid medium; (2) low moisture contents (usually at 12 %) of solid matrices and (3)occurring in a natural state (Raimbault, 1998; Ooijkaas et al., 2000). The mycelialmorphology of actinobacteria which are used for SM production, is advantageous inout competing unicellular microorganisms for colonisation of solid substrates and forefficient utilisation of nutrients. Additionally the solid matrices enable theactinobacterial cultures to develop and differentiate along gradients. Table 17 lists theadaptation of SSF technology in the production of secondary metabolites byactinobacteria._____________________________________________________________________47