Factors Influencing Allelopathy and Toxicity in Prymnesium parvum¹

Abstract

Some microalgae are able to kill or inhibit nutrient-competing microalgae, a process called allelopathy. Inhibiting or killing competitors enable these species to monopolize limiting resources, such as nitrogen and phosphorus. Prymnesium parvum is known to produce such allelopathic compounds, substances that seem identical to the ichthyotoxins identified from this species. Biotic and abiotic environmental factors influence not only growth rates but also toxin ⁄ allelopathic compounds production by P. parvum cells. Toxin production, as well as allelopathy, including grazer deterrence, increases dramatically in light, temperature, or nutrient stressed P. parvum cells. Correspondingly, toxicity and allelopathy may decrease, or cease completely, if cells are grown with high amounts of N and P in balanced proportions. However, even under nutrient (N and P) sufficient conditions, P. parvum is able to produce toxins ⁄ allelopathic compounds, with negative effects on other phytoplankton species or grazers, if cells densities of P. parvum are high relative to other species. This negative effect might shift the plankton community to more toxin resistant species. Filtrates from nutrient-deficient P. parvum cultures have almost the same strong negative effect on grazers and other phytoplankton species as when Prymnesium cells are grown together with the target organisms. Eutrophication, the increased input of N and P to aquatic ecosystems, besides increasing nutrient concentrations, is usually provoking unbalanced N:P condition for the optimal growth of phytoplankton, deviating from the Redfield ratio, i.e., the phytoplankton cellular nitrogen to phosphorus ratio, N:P = 16:1 (by atoms) or 7.2:1 (by weight). Eutrophication thus both enhances P. parvum growth and increases production of toxins and allelopathic compounds. Supplying N-deficient or P-deficient P. parvum cells with the deficient nutrient reduces toxicity to less than half within 24 h after additions. As P. parvum is mixotrophic, uptake of dissolved or particulate organic N (DON or PON) can also reduce toxicity and allelopathy in the same manner as addition of inorganic N to Nstarved cells. In conclusion, P. parvum, by increasing its toxicity and allelopathic ability under poor environmental conditions, outcompetes the co-occurring phytoplankton species.

Transcriptomic response of the toxic prymnesiophyte Prymnesium parvum (N. Carter) to phosphorus and nitrogen starvation

“…The organism produces and releases toxic substances even under nutrientreplete conditions, but toxicity is increased under abiotic or biotic stress conditions including limitation of inorganic nutrients, nitrogen [N] and especially phosphorus [P] (Freitag et al, 2011;Grané li and Salomon, 2010). Prymnesium parvum is not able to feed on motile prey (Skovgaard and Hansen, 2003); it is supposed therefore that the role of the induced allelopathic/toxic compounds is to immobilize and lyse competing and prey algal species (Tillmann, 1998) and potential grazers (Tillmann, 2003).…”

Hemolytic toxicity and nutritional status of Prymnesium parvum during population growth

“…Some studies have found that high pH increases the toxic activity of P. parvum (Shilo & Aschner 1953, while others have found the opposite (Padilla 1970, Igarashi et al 1998. Aeration can also increase the toxicity of P. parvum (Igarashi et al 1995), prompting suggestions that strong wind-mixing might enhance the toxicity of blooms (Granéli & Salomon 2010).…”

“…Factors associated with the toxicity of Prymnesium parvum were recently reviewed by Granéli & Salomon (2010). They proposed that the abundance and stage of population growth were important, with older and denser populations being more toxic than young, sparse populations.…”

“…Some studies have found that high pH increases the toxic activity of P. parvum (Shilo & Aschner 1953, while others have found the opposite (Padilla 1970, Igarashi et al 1998. Aeration can also increase the toxicity of P. parvum (Igarashi et al 1995), prompting suggestions that strong wind-mixing might enhance the toxicity of blooms (Granéli & Salomon 2010).In the present study, Prymnesium parvum was grown in P-limited batch cultures for 32 d with frequent sampling, to document the dynamics of cell abundance, cellular C, N and P composition, pH, and hemolytic toxicity. We hypothesized that toxic activity would rise appreciably as populations became phosphorus-limited, and we intended to resolve the timing of this event.…”

“…A bloom might never become nutrient-limited, but, even when it does, if toxic activity cycles with a period of 6 to 10 d, it might not be observed in samples taken to assess toxicity. Finally, ambient toxicity to aquatic organisms may vary with the many factors that commonly vary in inland waters, including salinity and temperature (Baker et al 2007), pH , and possibly bacterial abundance and activity (Granéli & Salomon 2010). …”