The haptophyte, Prymnesium parvum, produces ichthyotoxins that can significantly disrupt biodiversity and affect coastal economies reliant on fishing, aquaculture and tourism. Interactions between microalgae and associated bacterial communities play a key role in influencing phytoplankton metabolism and physiology. This study focuses on understanding how environmental conditions shape mutualistic interactions between P. parvum and its associated bacteria.

To investigate the physiology and metabolism of both the algae and bacteria within the holobiont concept, co-cultures of P. parvum and a synthetic bacterial community were performed under various nutrient-limited conditions in photobioreactors. Culture monitoring, metabarcoding, metatranscriptomic and metabolomic analyses were conducted to assess the dynamics of both the algal and microbial communities. The results show that depending the nutrient conditions, the interactions can range from neutral to beneficial, enhancing both the growth of microbial communities and the harmful capacity of P. parvum.

These findings pave the way for further functional analyses and metabolic networks. Understanding the interactions between P. parvum, bacteria and environment contributes to a more comprehensive view of the ecological impacts of P. parvum blooms.