Stress Response in Toxic Diatoms: The Effects of Abiotic Factors on Growth and RNA Content in <i>Pseudo-nitzschia calliantha</i> and in <i>Pseudo-nitzschia multistriata</i>
2023
Luca Ambrosino | Marco Miralto | Lucia Barra | Angela Sardo | Maria Luisa Chiusano | Radiana Cozza | Michele Ferrari | Silvestro Greco
Pennate diatoms belonging to the genus <i>Pseudo-nitzschia</i> are important components of phytoplankton assemblages in aquatic environments. Among them, the bloom-forming species <i>Pseudo-nitzschia calliantha</i> and <i>Pseudo-nitzschia multistriata</i> are known as domoic acid producers, and are thus considered harmful for aquatic organisms and for human health. For these reasons, monitoring the abundance of such species, as well as identifying the growth conditions enhancing or inhibiting their growth, could help to predict eventual risks for aquatic communities and for humans by direct or indirect exposure to these toxic algae. In this work, we assessed the effects of different parameters (irradiance, temperature, salinity, and nutrients) on six <i>Pseudo-nitzschia</i> species by evaluating their specific growth rates and total RNA content. Our results—corroborated by statistical analyses of regression and correlation plots of control samples and samples exposed to stressful conditions, showed, as expected, a general decrease in growth rates under suboptimal levels of temperature, irradiance, salinity, and nutrient supply (especially under silicon depletion), that was usually accomplished by a general increase in RNA content inside cells. We hypothesized that increments in RNA levels in cells exposed to unfavorable conditions could be due to a relatively fast activation of the mechanisms of stress response.
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