Evidence for induced allelopathy in an isolate of Coelastrella following co-culture with Chlorella sorokiniana

Despite the potential of microalgae to meet growing societal demands for food, fuel, and nutraceuticals, the industrial economics of production systems are limited by low crop productivity and stability driven, in part, by invading pests such as competing algae. Effective management strategies to mitigate this challenge rely on a clear understanding of the interactions between microalgal production strains and invaders. Here, we take advantage of the invasion of Chlorella sorokiniana culture in the field by a wildtype organism later isolated and identified as a Coelastrella species to better understand the dynamics between these strains. In a set of experiments focused on invasibility, we found that coexistence of strains was possible, but that Coelastrella was the competitive dominant. To determine if this advantage was due to allelopathic interactions, we grew both strains in media that contained cell-free exudates from monocultures of Coelastrella, monocultures of Chlorella, or co-cultures of both strains. Coelastrella exudates did not inhibit the growth of Chlorella, but exudates from the co-culture of both strains did. Chlorella also exhibited some self-inhibition to its own exudate at high concentrations. This work demonstrates the potential for inducible allelopathic interactions between two phytoplankton strains. Future work focused on this phenomenon, through metabolomic and metagenomic lenses, would greatly contribute to our understanding of allelopathy in aquatic systems.