The effects of salinity on the cellular permeability and cytotoxicity of Heterosigma akashiwo

Abstract

A laboratory study using the fish-killing raphidophyte Heterosigma akashiwo was conducted to examine its capability to grow at salinities below oceanic, and to test the perceived relationship between reduced salinities and increased cytotoxicity. A nonaxenic strain of H. akashiwo isolated from the U.S. Pacific Northwest was exposed to a combination of three salinity (32, 20, and 10) and five temperature (14.7°C, 18.4°C, 21.4°C, 24.4°C and 27.8°C) conditions. Our results demonstrate that cell permeability and cytotoxicity are strongly correlated in unialgal cultures of H. akashiwo, which both increased as salinity decreased from 32 to 10. Furthermore, over a broad median range of salinities (10 and 20), neither temperature nor specific growth rate was correlated with cytotoxicity. However, in cultures grown at the salinity of 32, both temperature and specific growth rate were inversely proportional to toxicity; this relationship was likely due to the effect of contamination by an unidentified species of Skeletonema in those cultures. The presence of Skeletonema sp. resulted in a cytotoxic response from H. akashiwo that was greater than the response caused by salinity alone. These laboratory results reveal the capability of H. akashiwo to become more toxic not only at reduced salinities but also in competition with another algal species. Changes in cell permeability in response to salinity may be an acclimation mechanism by which H. akashiwo is able to respond rapidly to different salinities. Furthermore, due to its strong positive correlation with cytotoxicity, cellular permeability is potentially associated with the ichthyotoxic pathway of this raphytophyte.

Seasonal variation in estuarine phytoplankton viability and its relationship with carbon dynamics in the Baltic Sea

“…Another possible explanation for this is that single species blooms may escape the important mortality-inducing factors such as allelopathy (Vardi et al, 2002;Poulin et al, 2018). Increased production of allelopathic chemicals might be induced by the presence of competing species (Ikeda et al, 2016). Also, the polyunsaturated aldehydes released by diverse phytoplankton, especially diatoms (Wichard et al, 2005), have been shown, among other effects, to cause membrane permeability in other phytoplankton species (Casotti et al, 2005;Ribalet et al, 2007).…”

Insights into Cellular Localization and Environmental Influences on the Toxicity of Marine Fish-Killing Flagellate, Heterosigma akashiwo

“…The ichthyotoxic raphidophyte Heterosigma akashiwo , a golden–brown unicellular microalga causing harmful algal blooms, has been frequently observed in coastal waters around the world over the past few decades [ 1 , 2 , 3 , 4 ]. H. akashiwo blooms are sporadic and are responsible for the fatality of cultured and wild fish in different parts of the world such as North America (including Canada and the United States) [ 4 , 5 , 6 , 7 , 8 ], Mexico [ 9 ], Japan [ 10 , 11 ], Chile [ 12 ], China [ 13 ], New Zealand [ 14 ], Europe (such as Spain) [ 15 ], and Norway [ 16 ].…”

“…Different environmental factors affect toxin production depending on the HABs taxon [ 11 , 30 , 31 , 32 , 33 , 34 ]. A direct correlation was detected between environmental factors such as light, temperature and salinity and the growth and toxicity of H. akashiwo in different geographical areas [ 3 , 10 , 11 , 23 , 24 ]. For the Japanese strain the highest toxicity was observed at a light intensity of 200 μmol photons m −2 s −1 , and a temperature lower than 25 °C [ 10 ].…”

“…For the Japanese strain the highest toxicity was observed at a light intensity of 200 μmol photons m −2 s −1 , and a temperature lower than 25 °C [ 10 ]. The highest cellular toxicity of H. akashiwo (NWFSC-513) which was isolated from the bloom in 2010 in the Salish Sea, the inland waters of southwestern British Columbia, Canada, and northwestern Washington, USA, was detected at a temperature of 14.7 °C and a salinity of 32 [ 3 ]. The bloom of H. akashiwo was observed for the first time in Red Sea waters, off the coast of Saudi Arabia in May 2010.…”

Yeast Cell as a Bio-Model for Measuring the Toxicity of Fish-Killing Flagellates

“…Using mice as a bioassay models has been debatable since they were first used, due to unreliability and the associated ethical issues [43,44]. Various cell lines obtained from different animals including a mouse [45], a rat [34], fish gill cells [46][47][48][49], or human tissues such as human hepatoma cell line (HepG2) [50], or human colon carcinoma cell line (Caco-2) [51], are recommended and have been used to measure different types of toxins produced by algal bloom species. Using whole organisms or their cell lines as a bioassay model for ichthyotoxicity measurement obligates prolonged exposure or follow-up periods, and therefore increases the errors in evaluation.…”