Abstract
Cylindrospermopsis raciborskii is a potentially toxic freshwater cyanobacterium that can tolerate a wide range of light and temperature. Due to climatic changes, the interaction between light and temperature is studied in aquatic systems, but no study has addressed the effect of both variables on the saxitoxins production. This study evaluated the combined effect of light and temperature on saxitoxins production and cellular quota in C. raciborskii. Experiments were performed with three C. raciborskii strains in batch cultures under six light intensities (10, 40, 60, 100, 150, and 500 μmol of photons m−2 s−1) and four temperatures (15, 20, 25, and 30 °C). The growth of C. raciborskii strains was limited at lower temperatures and the maximum growth rates were obtained under higher light combined with temperatures equal or above 20 °C, depending on the strain. In general, growth was highest at 30 °C at the lower light intensities and equally high at 25 °C and 30 °C under higher light. Highest saxitoxins concentration and cell-quota occurred at 25 °C under high light intensities, but were much lower at 30 °C. Hence, increased temperatures combined with sufficient light will lead to higher C. raciborskii biomass, but blooms could become less toxic in tropical regions.
Highlights
Cylindrospermopsis raciborskii is a freshwater cyanobacterium, which is widely distributed in tropical, subtropical, and temperate regions [1,2]
CYLCAM-01 strain exhibited the highest growth rates (p < 0.05) at 25 ◦ C when combined with 100 μmol photons m−2 s−1, reaching 0.58 ± 0.03 day−1 (Figure 1A1,A2)
The C. raciborskii strains in this study demonstrated a great tolerance to grow over a wide range of light and temperature, where they obtained maximum growth rates in high light intensities combined with temperatures ≥20 ◦ C
Summary
Cylindrospermopsis raciborskii is a freshwater cyanobacterium, which is widely distributed in tropical, subtropical, and temperate regions [1,2] It can tolerate a wide range of temperatures and light intensities [3,4,5] and is able to produce distinct cyanotoxins, like cylindrospermopsins (CYN) and saxitoxins (STXs) [6]. The production of these cyanotoxins by C. raciborskii is related to its geographical distribution, where Brazilian strains produce STX derivatives [7,8,9] and Australian strains can produce. Environmental factors that have been found upregulating STX biosynthesis are high light intensity [7], high and suboptimal temperature, extracellular salt (NaCl) [19], conductivity, and dissolved inorganic nitrogen (DIN) [20], whereas high nitrogen concentrations and darkness downregulated STX biosynthesis [7,19]
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