Co-Culture of Cyanobacteria and Rhizobia, Increasing Biomass Under Nitrogen-Starvation Conditions.

A pair of new strains was obtained from a natural environment and identified as the filamentous non-heterocystous cyanobacterium SZ2 and the rhizobia Ensifer/Sinorhizobium sp. ST1. This pair was of particular interest because it could potentially perform both photosynthesis and nitrogen fixation. Interactions and material production were investigated in a new co-culture system using the "natural pair" of these strains. Cocultivation was favorable under both mixotrophic (coMC) and autotrophic conditions (coAC) when material production was assessed using heptadecane (CH) from the SZ2 strains. Under coAC, where nitrogen is depleted, some soluble factor(s) produced by the co-culture-possibly including ammonium ions-appear to function as biomass-increasing factors (BIFs), contributing to the enhanced accumulation of chlorophyll a in SZ2, along with extracellular polysaccharides, lipids, carbohydrates, and proteins in the total biomass. A notable feature of this "aquatic" coAC system is that it overcomes biomass reduction under nitrogen-deficient conditions, which is difficult in monoculture systems and can contribute to economic material production for biorefineries.