Effects of oligosaccharides and polysaccharides on the generation of reactive oxygen species in different biological systems.

Use of carbohydrates as elicitors is a novel technique for enhancement of the production of industrially important microbial products. The relation between the levels of ROS (reactive oxygen species) and overproduction of antibiotics in microbial cultures has already been established. In the present study, we aimed to exploit the ROS response to develop a fast technique to assess the potential of oligosaccharides [oligoguluronate, oligomannuronate and MO (mannan oligosaccharides)] and polysaccharides [alginate and LBG (locust-bean gum)] as elicitors for overproduction of secondary metabolites in Streptomyces rimosus and Penicillium chrysogenum. We have also investigated changes in the production of ROS in neutrophils as a result of the action of the same elicitors. LBG-derived oligosaccharides (MO) were most potent inhibitors of ROS in all systems investigated. This correlates with overproduction of secondary metabolites in microbes and enhancement of a number of mammalian systems. We believe that the effects of oligosaccharides and polysaccharides on ROS production by mammalian and microbial cells can be correlated predicatively with overproduction. The underlying methodology offers a fast screening of elicitors that can be applied across the different systems.

Elicitor effects on Penicillium chrysogenum morphology in submerged cultures.

Changes in morphology and sporulation were investigated in liquid cultures of Penicillium chrysogenum P2 supplemented with carbohydrate oligosaccharides. Sodium alginate and locust-bean (Ceratonia siliqua) gum-derived oligosaccharides were used as elicitors. Spore germination was inhibited by the addition of OG (oligoguluronate) elicitor (30% inhibition when compared with control). Addition of any of the elicitors to stirred-tank cultures increased hyphal-tip numbers, clump area and spore counts. MO (mannan oligosaccharide) had the greatest effect on the parameters studied, followed by OM (oligomannuronate) and OG. Hyphal-tip numbers increased by 19, 29 and 47% with OG, OM and MO respectively. Average clump area in the presence of OG, OM and MO increased by 23, 32 and 59% respectively. A notable increase in spore numbers was observed in all the supplemented stirred-tank reactor cultures, with MO showing the highest enhancement.

Elicitation of plants and microbial cell systems.

Plants show physiological and morphological responses to a range of physical and chemical factors known as 'elicitors'. These responses have been considered as defence reactions 'elicited' by the plants' biochemical factory to ensure their survival, persistence and competitiveness. Recently examples have been cited of elicitation in some fungal and bacterial cultures. Through a chronological survey, this Review considers examples of elicitors and elicitation and describes suggested mechanisms of elicitation in plants and microbial cell cultures. The majority of research in this field has been carried out on the plant systems using complex (undefined) biotic elicitors. Carbohydrates are the main class of compounds used as defined elicitors. This Review focuses on carbohydrates as compounds initiating a defence response in cell cultures. Physiological changes brought about on the plant and microbial cultures include expression of novel metabolites and overproduction of already known products. Recent reports confirming elicitation in microbial cultures are of potential importance, as the relative ease of fermentation and scale-up could open an opportunity for the introduction of useful novel metabolites as well as enhancement of commercially useful bioproducts. In this context, a sound knowledge of the elicitor molecules' structure-function relationships and mechanisms of elicitation is essential.