Abstract
Prymnesium parvum is a toxin-producing microalga, which causes harmful algal blooms globally, frequently leading to massive fish kills that have adverse ecological and economic implications for natural waterways and aquaculture alike. The dramatic effects observed on fish are thought to be due to algal polyether toxins, known as the prymnesins, but their lack of environmental detection has resulted in an uncertainty about the true ichthyotoxic agents. Using qPCR, we found elevated levels of P. parvum and its lytic virus, PpDNAV-BW1, in a fish-killing bloom on the Norfolk Broads, United Kingdom, in March 2015. We also detected, for the first time, the B-type prymnesin toxins in Broads waterway samples and gill tissue isolated from a dead fish taken from the study site. Furthermore, Norfolk Broads P. parvum isolates unambiguously produced B-type toxins in laboratory-grown cultures. A 2 year longitudinal study of the Broads study site showed P. parvum blooms to be correlated with increased temperature and that PpDNAV plays a significant role in P. parvum bloom demise. Finally, we used a field trial to show that treatment with low doses of hydrogen peroxide represents an effective strategy to mitigate blooms of P. parvum in enclosed water bodies.
Highlights
In a world with a rapidly growing human population, it has been estimated that since 1961 the average annual increase in consumption of fish (3.2%) has outpaced human population growth (1.6%), with further increased demand expected for the coming decade.[1]
We sought to detect the prymnesin toxins from environmental water samples. They are implicated in fish mortality worldwide and have previously been extracted and detected from laboratory-grown cultures of P. parvum, the prymnesins have yet to be detected from environmental water samples or from their speculated targets
We took a multidisciplinary approach to learn more about bloom dynamics and the bloom microbiome of this harmful alga and its lytic virus, PpDNAV, and provide potential solutions and future management strategies for blooms of this organism
Summary
In a world with a rapidly growing human population, it has been estimated that since 1961 the average annual increase in consumption of fish (3.2%) has outpaced human population growth (1.6%), with further increased demand expected for the coming decade.[1]. The biotic factors that impact P. parvum growth and toxicity have been studied extensively in laboratory settings.[5−7] there has been speculation regarding the toxic entity responsible for fish deaths,[8] an increasing body of research has been focused on the ichthyotoxins (prymnesins) due to their structural similarity to other ladder-frame polyether phycotoxins.[9] the prymnesins have not previously been detected in a natural setting. First isolated by Igarashi and co-workers in 1995,10−12 the prymnesins are a group of polyketide metabolites that display potent ichthyotoxicity (Figure 1). Since their discovery, a chemically diverse family of prymnesins, including prymnesinB1, have been discovered,[13−15] largely differing in the polyether core, glycosylation patterns, and level of chlorination of the toxins.
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