In situ carbon dioxide fixation in the process of natural astaxanthin production by a mixed culture of Haematococcus pluvialis and Phaffia rhodozyma

In order to fix CO2 generated by microbial fermentation, two astaxanthin over-producing microorganisms, the green alga Haematococcus pluvialis and the red yeast Phaffia rhodozyma, were mix-cultivated in the same media. CO2 from P. rhodozyma fermentation was fixed by H. pluvialis simultaneously in the process of photosynthesis, while O2 produced by H. pluvialis in photosynthesis stimulated astaxanthin formation in P. rhodozyma. As a result, both concentrations of biomass and astaxanthin increased significantly compared to the pure cultures of the two species. The maximum concentrations of biomass and astaxanthin, 5.70 g/l and 12.95 mg/l, were obtained by the mixed culture. This culture strategy provides a novel way for improving the yield of higher valued bio-product with in situ CO2 fixation.