Biomass of Microalgae and Other Phototrophic Microorganisms: Current Trends in Regulation of Its Accumulation and Application of Immobilized Forms

The current interest in microalgal biomass does not subside but continues to intensify due to the emergence of new trends in the use of this bioresource in various biotechnological and environmental processes. The rather slow growth rate of phototrophs compared to other microorganisms limits more active application of the biomass for various purposes. Stimulation of the Quorum Sensing formation in the cells due to the appearance of their own quorum molecules or those produced by other co-cultured microorganisms in the medium is one of the efficient approaches for overcoming this limitation. This review discusses the immobilization or co-immobilization of phototrophic cells with other microorganisms as an effective way to maintain accumulation of the target biomass for long-term period at improved rates. The 40% increase in the use of co-immobilized phototrophs for biomass obtaining and its use in wastewater treatment has been observed over the past five years. The level of investigations of co-immobilized microalgae cells is four times higher than that of the immobilized single cultures. Among the main trends in the new investigations of immobilized forms of microalgae, the predominant application of Chlorella genus cells in immobilized samples of individual cultures and the involvement of diatom microalgae and cyanobacteria, in addition to Chlorella cells, in co-immobilization with other microorganisms, was ascertained. The most significant increase in the rate of microalgal biomass accumulation uncovered in cases of co-immobilization of microalgae with bacteria. In several cases, in the presence of bacteria, co-immobilization has led to the emergence of new characteristics in microalgal cells (increased synthesis of pigments, polysaccharides, biofilm formation, etc.), which opens new directions for their further practical use as biopesticides, components of packaging and building materials, etc.