افزایش تولید گلوکز اکسیداز توسط پنیسیلیوم ویبرین P16 Enhancement of glucose oxidase production by Penicillium variabile P16

While elicitation of metabolites has been established in bacterial, plant, and cell cultures, very little information is available on the elicitation effect of fungal cultures. In a previous paper 6 , we reported for the first time the enhancement of a secondary metabolite, penicillin G, production in cultures of Penicillium chrysogenum strain P2 using oligosaccharides OG and OM obtained from alginate. While changes in the physiological activities induced by alginate oligosaccharides have been established in reports on bacterial, animal, and in particular, plant systems,5,9,23 ] 25 relatively little information is available on the elicitation effect of intact alginate. Dornenburg and Knorr 2,7 ¨ described the enhancement effect of microbial alginate on anthraquinone synthesis in Morinda citrifolia cultures; however, the authors observed no elicitation when LBG and alginate of plant origin were used. Also, enhancement of sesquiterpene synthesis in plant cell cultures of Hyoscyamus muticus has been reported.26 In this paper, we have investigated the effect of polyand oligosaccharides on the enhancement of the production of GOD, an enzyme of commercial importance,10,11,16 by P. ¨ariabile P16. While enhancement of penicillin G yield has been detected after addition of OG and OM blocks with a DP of approximately ten 6 no considerable increase was observed in GOD activity based on biomass cell Ž dry weight from . P. ¨ariabile under similar elicitation conditions; however, the enhancement was significant Ž . increases up to approx. 70% after addition of alginate. This suggests that enhancement of metabolic activity in fungi by OM and OG blocks of the same DP is not generic. While elicitation occurs in the presence of these blocks, the degree of polymerization plays a very important role in the enhancement of the desired metabolites. The reason for this is not clear at present. It is likely that the oligosaccharides must bind a receptor which is probably located on the cell membrane in order to enhance the production of GOD and other secondary products. The fact that only oligosaccharides of a specific size range exert this effect suggests that the receptor has a well-defined shape, akin to mammalian receptors, for instance, for mannose-6- phosphate. The intracellular consequences of binding to the receptor are initiated by the synthesis of cyclic AMP and the modulation of the activities of enzymes and control proteins, resulting in the activation of other enzymes probably activated allosterically by cAMP. Further studies are needed to elucidate the reasons for the change in the metabolism of the fungi. In conclusion and in agreement with the suggestion made in our previous paper,6 it seems that alginate and its oligosaccharides function as activators of defensive systems in P. ¨ariabile. In fact, GOD activity can play, in combination with other mechanisms of biocontrol, a significant role in antiobiosis in the soil environment: 27,28 the hydrogen peroxide enzymatically produced is cytotoxic for living organisms.29 The growth of many bacterial and fungal species is thus inhibited in thepresence of GOD30,31 which, e.g., killed microsclerotia of Verticillium dahliae both in ¨itro and in sterile soil.28 The probable presence of alginate of microbial origin in carbohydrate-rich areas32 might represent a biological signal to enhance GOD fungal production, thus increasing the competitiveness of such fungi.