Browsing by Author "Mardones, Jorge, I"

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    Heterosigma akashiwo in Patagonian Fjords: Genetics, Growth, Pigment Signature and Role of PUFA and ROS in Ichthyotoxicity
    (2022) Flores-Lenero, Ana; Vargas-Torres, Valentina; Paredes-Mella, Javier; Norambuena, Luis; Fuenzalida, Gonzalo; Lee-Chang, Kim; Mardones, Jorge, I
    Heterosigma akashiwo is the only raphidophyte described for Chilean waters. A recent 2021 fish-killing bloom event of this raphidophyte ignited scientific research, but the ichthyotoxic mechanism and environmental conditions that promote its growth are still unclear. This is the first study confirming the occurrence of H. akashiwo in Chilean waters on the basis of the region D1/D2 of the 28S ribosomal gene. The pigment signature of the CREAN_HA03 strain revealed chlorophyll-a, fucoxanthin, and violaxanthin as the most abundant pigments, but profiles were variable depending on culture and field conditions. A factorial temperature-salinity growth experiment showed a maximal growth rate of 0.48 d(-1) at 17 degrees C and 35 in salinity, but reached a maximal cell abundance of similar to 50,000 cells mL(-1) at 12 degrees C and 25 in salinity. The fatty acid profile included high levels of saturated (16:0) and polyunsaturated (18:4 omega 3; 20:5 omega 3) fatty acids, but superoxide production in this strain was low (similar to 0.3 pmol O2- cell(-1) h(-1)). The RTgill-W1 bioassay showed that the H. akashiwo strain was cytotoxic only at high cell concentrations (>47,000 cells mL(-1)) and after cell rupture. In conclusion, salmon mortality during H. akashiwo bloom events in Patagonian fjords is likely explained by the high production of long-chain PUFAs at high cell densities, but only in the presence of high ROS production.
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    Salinity-Growth Response and Ichthyotoxic Potency of the Chilean Pseudochattonella verruculosa
    (2019) Mardones, Jorge, I; Fuenzalida, Gonzalo; Zenteno, Katherine; Alves-de-Souza, Catharina; Astuya, Allisson; Dorantes-Aranda, Juan Jose
    Despite salmon farmers suffering the worst damage from a harmful algal bloom in Chile's history (US$800M) due to a massive outbreak of the dictyochophyte Pseudochattonella verruculosa in 2016 (similar to 7000-20,000 cells ml(-1)), the effect of environmental drivers and the potency of lytic toxins produced by the local clones of this species remain still largely unexplored. Based on the drastic oceanographic anomalies observed in the Chilean fjords during the 2016-El Nino "Godzilla" event, the role of salinity (15 to 35 psu) on Pseudochattonella cell growth and cytotoxicity was studied by culturing, scanning electron microscopy (SEM) and using a rainbow trout cell line RTgill-W1 assay to define: (1) vegetative growth rates, (2) cell taxonomy, (3) ichthyotoxicity of monoclonal cultures at 25 and 35 psu in salinity, (4) differences in toxicity of lysed cells and supernatant at different cell concentrations (from 10 to 100,000 cells ml(-1)), and (5) temporal stability of lytic compounds. This study formally confirms the presence of P. verruculosa in Chilean waters using the large subunit (LSU) of the nuclear ribosomal RNA gene. The Chilean P. verruculosa ARC498 strain showed maximum cell densities at 30 psu (max. 84,333 +/- 4,833 cells ml(-1)) and maximum growth rates (mu(max)) at 20 psu (1.44 cells d(-1)). Cultures at 15 psu showed suppressed maximum cell density (max. 269 +/- 71 cell ml(-1)) but high mu(max) were recorded at the beginning of the exponential growth (1.31 cells d(-1)). No significant differences were observed between lysed cells and supernatant treatments in the two salinity levels, suggesting that the most lytic portion is released into the cell-free media instead of remaining cell bound. Cytotoxicity was correlated to cell abundance, reducing gill cell viability down to 80 and 65% compared to controls at 10,000 and 100,000 cells ml(-1), respectively. Unexpectedly, lytic compounds from P. verruculosa ARC498 at 35 psu showed to be less toxic than cultures at 25, where a noticeable presence of peripheral mucocysts were observed by SEM. Lytic compounds from in vitro experiments are weakly toxic even at high cell concentrations, highly unstable and rapidly degraded in the light after 5 days of storage at 15 degrees C. Our results point to the important effect of salinity on growth and ichthyotoxic potency of Pseudochattonella species and highlight the need for a deeper insight into the role of mucocysts in fish gill damage, which would provide a greater understanding as to the harmful modes of action of this species.