Kirpenko N. Mechanisms of biotic interaction between freshwater microalgae

Regularities and mechanisms of biotic interaction between species were revealed on the example of mixed cultures of green and blue-green freshwater algae. It has been found that interaction is registered both within the same ecological group (phytoplankton) and between different ecological groups (phytoplankton and phytoperiphyton), between closely related species and those differing in their taxonomic affiliation, and under different environmental conditions. Interaction between algae is species-specific and depends on their physiological state. Changes in the intensity of algae growth as a result of interaction are accompanied by transformations in physiological and biochemical processes, including photosynthesis, respiration, accumulation of extracellular organic matter, changes in the content of endo- and exogenous proteins and in the redistribution of their fractional composition, and the formation of substances non-typical to monocultures. The most essential disruptions are observed at the early stages of the contact between the cells of different species. Changes in the activity of endo- and exogenous oxidation-reduction enzymes (nitratereductase and catalase), in the intensity of free-radical processes, and in the accumulation of lipid peroxidation products are indicative of the formation of oxidative stress. The response of algae to the influence of other species is closely similar to non-specific adaptation syndrome of cell systems. During the process of interaction algae are capable of transforming exometabolite composition. The media of the studied mixed cultures unlike the media of monocultures were characterized by the presence of benzoic acid and by the increase in the content of dihydromethyljasmonate. These substances are capable of transforming metabolism and inducing protective reactions responsible for the increase in the resistance of algae to the influence of other species.