Culture study on utilization of phosphite by green microalgae

摘要

The continuous decline in phosphorus (P) resources is a serious global issue. Therefore, it is important to develop methods to recover P from waste and wastewater. Most P ores are currently used in the phosphate form in the agriculture industry and in detergents, which results in a large release of phosphates into natural aquatic environments. Much attention has been given to measuring phosphate levels and monitoring water quality, survey, and control of algal phytoplankton dynamics. However, phosphite is oxidized from hypophosphite after plating and discharged as waste, so methods to recycle and reuse phosphite should also be developed. Currently, there is no evidence of phosphite utilization by photosynthetic eukaryotes, including eukaryotic algae. Thus, except for the possible utilization by some bacteria when phosphate is unavailable, the fate of the phosphite that is discharged is mostly unknown. Chlorella vulgaris (NIES-2170), Coccomyxa subellipsoidea (NIES-2166), Scenedesmus obliquus (NIES-2280), and Botryococcus braunii (BOT-22) were cultured in phosphite medium under conditions that prevented phosphate contamination and phosphite oxidation. As a result, the number of C. vulgaris and C. subellipsoidea increased in the phosphite medium, demonstrating the availability of phosphite for the growth of these strains. In particular, the growth of C. vulgaris increased as the phosphite concentration increased. After being cultured for 180 days in photosynthetic conditions, phosphite utilization rates were 32-38%. In contrast, S. obliquus and B. braunii strains did not grow in the phosphite medium. In conclusion, C. subellipsoidea and C. vulgaris utilize phosphite as a P resource, which is a novel finding in photosynthetic eukaryotes. The results of this study may have important implications for the phosphorus redox cycle.