Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 4: DISCUSSIONinterference of ammonium on synthases of secondary metabolism, which can begenerated by rapidly utilizable nitrogen sources such as inorganic ammonium salts(Braña & Demain, 1988). It has been shown that organic nitrogen sources promote theenhancement of polyene type antibiotics (Kim et al., 2001). It was shown that SBMhad a superior effect in actinobacterial fermentations, however when combined withanother natural source of nitrogen YME minimal antimicrobial activity was attained.This may indicate an excessive use of nitrogen sources which is known to represssecondary metabolite production, alternate sources of nitrogen or elimination of onenitrogen source may have alleviated repression (Demain, 1995)4.2.2.3 Suitability of liquid media for secondary metabolite screeningIt was evident that certain media, secondary metabolites exerted antibacterial and antifungalactivity (dextrin and medium 153) whereas other media exhibited narrowspectrum activity against either bacteria (medium IM25) or fungi (medium 153m).Commonalities between the medium used by Saadoun and Al-Momani (2000) withmedium 153 which both contain beef extract-peptone-glucose as the major ingredientshas been shown to induce specific antifungal activity, this was evident in ourexperiments. Directed screens could serve to benefit from the implication of mediatypes such as #153 expressing SM with a desired biological activity, and eliminatingcultures not expressing this activity in specific media.4.2.2.4 Effect of Oil Supplementation to Submerged FermentationsFurther evaluations incorporating novel approaches to improving cultivationconditions for SM screening involved utilizing oil supplementation. In this study alleight different oils showed good antimicrobial activities (>20mm) at testedconcentration of 3 % (w/v), however vegetable, safflower and soybean oils producedhigher antibacterial activities (Table 53). This observation is in agreement with otherantibiotic fermentations where addition of high level supplementation from 2 % to10 % (w/v) vegetable oils in complex media enhances production of SM (Jia et al.,1999). In contrast it has been shown that low level supplementation at a concentrationof 0.05 % (w/v) vegetable oils particularly soybean and sunflower oils act asadjuvants improving consumption of carbon sources and increasing production ofantibiotics (Jones & Porter, 1998)._____________________________________________________________________123