A.H. Tambiev

The considerable position among organic exometabolites, excreted into medium, belongs to car-bohydrates. Their concentrations differ depending on species of alga, which contain as polysac-charides as monosaccharides, which can be absorbed by attendant bacterium and in these way form the trophic connections between species. In for theirs turn bacterium can excrete the carbo-hydrates into medium, as their own exometabolites. The work was made with axenic and algologically pure cultures of microalga Platymonas viridis Rouch, which are the prospective object of mass cultivation. It was demonstrated, after obtaining axenic culture, that algologically-pure culture accompanies with one species of bacteria, which was obtained in pure form and both of them make up the natural alga-bacterium association. During their growth axenic and algologically-pure culture did not differ almost. During the gas-liquid chromatographic determination of composition of extracellular monosac-charides and polysaccharides in the form of acetates of polyols, was shown, that attendant bacte-rium take up selectively certain carbohydrates, released into medium by both axenic and algologi-cally-pure culture. Xylose, galactose, mannose were absorbed, rhamnose and arabinose were not absorbed by them. Bacterium include mannose into composition of their polysaccharides, which excreted into medium later. Such selective absorption of carbohydrates by bacterium demonstrates trophic interaction between the two partners of a natural alga-bacterium association and begins in logarithmic phase of alga growth when the considerable increase of accompanying bacterium cells are observed.