Effects of Plastid Acquisition on Toxin Production in Marine Food Chains
Differential equation model for cryptophyte-Mesodinium-Dinophysis food chain. Left: Diagram of flows of material and plastids through the food chain. We used a two-stage representation of both Mesodinium and Dinophysis in which photosynthetic (P subscript) and heterotrophic (H) subscripts are represented as two life stages. Ciliates and dinoflagellates transition between these stages through predation events that lead to plastid acquisition, and through photosynthetic reproduction and plastid loss. Right: The model’s dynamics are highly sensitive to light, with increasing light levels allowing for the persistence of higher trophic levels and, ultimately, the development of cyclic dynamics (limit cycles).
This project quantifies the effects of acquired metabolism on toxin production in aquatic food webs. We study a three-part metabolic acquisition: Cryptophyte algae contain chloroplasts that are stolen by ciliates from the genus Mesodinium; in turn, dinoflagellates from the genus Dinophysis steal the chloroplasts from Mesodinium. The end member (Dinophysis) in this CMD food chain is a toxin-producing harmful alga that produces okadaic acid and dinophysistoxin, which can bioaccumulate in the marine food chain and lead to shellfish poisoning. Dinophysis toxin production and toxin content varies with growth rate: “stationary phase” cells (characterized by nutrient limitation, dense populations, and high stress) produce and contain higher amounts of toxin. Because Dinophysis grows photosynthetically using stolen chloroplasts, we are working to quantify the role of plastid origin and availability on toxin production, to better predict the environmental conditions under which toxin production is highest.
By quantifying the production of a harmful algal toxin, we identify the types of environmental conditions under which such toxins are likely to pose a threat to human health and livelihoods. Findings have implications beyond Dinophysis, to other chloroplast-stealing harmful algae such as Pfisteria piscicida. Second, by understanding how acquired photosynthesis is coupled to toxin production in Dinophysis, we gain insights into how we can engineer couplings of these acquisitions with other complex metabolic pathways of interest.
