Reducing nutrient requirement using nitrogen-fixing bacteria for microalgae cultivation

Abstract

In environments, microalgae have been observed to coexist with bacteria. Different nitrogen-fixing bacteria (NFB) were isolated from Armenian soils and their growth was evaluated in co-cultivation with the microalga Tetradesmus obliquus and cyanobacteria Synechocystis sp. PCC 6803. The most effective mutualistic consortium was T. obliquus-NFB5 (Sphingobacterium sp. L13G8). This resulted an increase in both populations, chlorophyll fluorescence, biomass protein, carbohydrate content, an effect on lipid metabolism, without the need for external nitrogen. The findings demonstrated the significance of employing NFB for microalga growth, as they facilitate the essential nitrogen provision in N-free Bristol medium. Moreover, in mutualistic consortia, microalgae facilitate the exudation of dissolved organic carbon and O₂ to bacteria, which, in turn, become available for bacteria, thereby reducing the necessity for energy-consuming aeration processes in co-cultivation. In return, the bacteria provide the microalgae with CO₂, B vitamins and demineralize N₂, P, S, thereby further supporting the growth of microalgae.