Study of the effects of oligosaccharides in liquid cultures of Penicillium chrysogenum
Oligosaccharides and polysaccharides have different effects on the morphology and production of secondary metabolites by Penicillium chrysogenum P2 (ATCC 48271). Addition Of oligosaccharides, derived from sodium alginate and locust bean gum, to submerged cultures of P. chrysogenum P2, at milligram per litre concentration (150 mgL-1), increased secondary metabolite levels and spore production, caused changes in morphology and gerRiination of spores, and affected the production of Reactive Oxygen Species. The source of the oligosaccharides controlled their effects on the cultures. Oligosaccharides when added to submerged cultures of P. chrysogenum P2 increased both penicillin G and extracellular levels of 6-aminopenicillanic acid concentrations. The oligosaccharides had no significant effects on biomass levels. Locust bean gum-derived oligosaccharides (mannan oligosaccharides, DP 5-8), showed the highest levels of enhancement in both penicillin G and 6-aminopenicillanic acid concentrations. Sodium alginate-derived oligosaccharides, (oligoguluronate, DP 7 and oligomannuronate, DP 7), also induced elicitation of penicillin G and 6-aminopenicillanic acid. Oligomannuronate was shown to be more effective than oligoguluronate. In P. chrysogenum P2 cultures mannan, oligomannuronate and oligoguluronate oligosaccharides enhanced yields of penicillin G by 101%, 78% and 59%, respectively. Addition of mannan, oligomannuronate and oligoguluronate oligosaccharides enhanced the levels of 6- aminopenicillanic acid by 39%, 26% and 19%, respectively. The addition of oligosaccharides and polysaccharides to spores of P. chrysogenum P2 in liquid medium had varying (inhibitory or stimulatory) effects on germination, germ-tube and clump development. The addition of oligosaccharides to submerged cultures of P. chrysogenum P2 showed effects on clump size and hyphal tip numbers. Mannan oligosaccharides had the greatest effect on morphology followed by oligomannuronate and oligoguluronate oligosaccharides. Oligosaccharides also speeded-up the sporulation and increased the concentration of spores of P. chrysogenum P2 in liquid cultures. Mannan oligosaccharides had the greatest effect followed by oligomannuronate and oligoguluronate oligosaccharides. 8-aminonaphthalene-1,3,6-trisulphonate-tagged oligosaccharide studies showed that the oligosaccharides pass through the cell wall of P. chrysogenum P2 suggesting a possible mechanism through modulation of gene function. The elicitation pattern was shown to be similar to untagged oligosaccharides. Oligosaccharides and polysaccharides were shown to inhibit production of Reactive Oxygen Species in P. chrysogenum P2. The highest level of inhibition was elicited by mannan followed by oligornannuronate and oligoguluronate oligosaccharides, and then locust bean gum and alginate. The results of the study showed the potential of oligosaccharides as elicitors of secondary metabolites in P. chrysogenum P2 as a filamentous fungus model. Understanding the elicitation mechanism could provide routes for ftirther exploitation of the potential of filamentous fungi in production of commercial products.