Microbiome Community Dynamics in Large Outdoor Algae Raceway Ponds

Abstract

Marine microalgae are photosynthetic microbes that are a potential source of fuels, animal feed, and other specialized products. Large scale cultivation of microalgae occurs in open, outdoor raceway ponds, which are exposed to the natural environment and these cultures quickly become a complex milieu of microbes. Microalgae interact with attached and free-floating bacteria found in their medium, with both positive and negative outcomes. To investigate the diversity and dynamics of microbes associated with these systems, samples were collected during multiple growth cycles of two biofuel-relevant microalgae strains, Desmodesmus sp. and Oocystis sp. in ~4,500 L outdoor raceway ponds. Microbiome community composition and diversity was dramatically different between ponds from the two algae and from the natural microbiome of the treated seawater used in pond medium. In spite of variable environments, the pond microbiomes were most similar to their inoculum PBR (photobioreactor) communities suggesting the importance of priority effects or environmental conditioning by the host algae. Ponds when both algae strains were grown were dominated by Rhodobacteraceae and Saprospiraceae while unhealthy microbiomes were dominated by Cytophagaceae and Puniceicoccaceae. Microbiome change was variable over time and resulted in different community structures at the time of algae harvest. Variation in the microbiome community structure was driven by the strain of algae grown, time, pond temperature and percent oxygen saturation. These results provide insight into this industrial ecology and are a foundation for future microbiome research to improve microalgae production.