Mutual supply of carbon and nitrogen sources in the co-culture of aerial microalgae and nitrogen-fixing bacteria

Abstract

This study investigated co-culture for supply of carbon (C) and nitrogen (N) sources by aerial microalgae and N-fixing bacteria. The aerial microalga Coelastrella sp. KGU-HN001 was isolated from the surface of steel signs in Japan. After examining monocultures of the microalga and N-fixing bacterium Rhodobacter sphaeroides, mutual nutrient supply was evaluated in co-culture using a medium without C and N sources. In co-culture under aerobic conditions, the cell number, biomass, total organic C in cells and the total N of cell suspensions increased. Carbohydrate was secreted from the microalga and nitrogenase activity was expressed by the bacterium. Addition of an N source enhanced N fixation in the co-culture. These results indicated that C and N fixation by the microalga and the bacterium occurred under aerobic conditions, and the microorganisms were able to grow by self-supplying nutrients even under nutrient deficiencies.