Auto-flotation of heterocyst enables the efficient production of renewable energy in cyanobacteria

Utilizing cyanobacteria as a bioenergy resource is difficult due to the cost and energy consuming harvests of microalgal biomass. In this study, an auto-floating system was developed by increasing the photobiological H-2 production in the heterocysts of filamentous cyanobacteria. An amount of 1.0 mu M of diuron, which inhibited O-2 production in cyanobacteria, resulted in a high rate of H-2 production in heterocysts. The auto-floating process recovered 91.71% +/- 1.22 of the accumulated microalgal biomass from the liquid media. Quantification analysis revealed that 0.72-1.10 mu mol H-2 per mg dry weight microalgal biomass was necessary to create this auto-floating system. Further bio-conversion by using anaerobic digestion converted the harvested microalgal biomass into biogas. Through this novel coupled system of photobiological H-2 production and anaerobic digestion, a high level of light energy conversion efficiency from solar energy to bioenergy was attained with the values of 3.79% +/- 0.76.