Combined Effect of Light and Temperature on the Production of Saxitoxins in Cylindrospermopsis raciborskii Strains

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.

Ecophysiological Aspects and sxt Genes Expression Underlying Induced Chemical Defense in STX-Producing Raphidiopsis raciborskii (Cyanobacteria) against the Zooplankter Daphnia gessneri

“…Different stress conditions can activate similar physiological responses as cyanotoxin production. Studies with both STX-and CYN-producing R. raciborskii strains have demonstrated this imbalance between growth and toxin production in response to abiotic stress (e.g., nutrient limitation, light and temperature stress) [30,[70][71][72]. However, our study is the first to report the response of the cyanobacterium R. raciborskii to biotic stress caused by predation.…”

“…Some strains of R. raciborskii can produce toxic alkaloids with neurotoxic (saxitoxins (STXs)) or cytotoxic activity (cylindrospermopsins (CYNs)). In South America, toxic strains have been reported to be STX producers [29][30][31][32][33], while no strain has been characterized to produce CYN, although some studies have detected this toxin in environmental samples [34]. Moreover, non-toxic R. raciborskii strains, which usually lack genes encoding STXs or CYN [35], can also be found in the environment, co-occurring with toxic strains.…”

Limnological Differences in a Two-Basin Lake Help to Explain the Occurrence of Anatoxin-a, Paralytic Shellfish Poisoning Toxins, and Microcystins

“…Because complex mixtures of cyanobacteria were so common, it is challenging to identify which of the genera may have been producing the observed toxins. Furthermore, high concentrations of toxins may be produced by minor genera found within a bloom, as environmental and biochemical factors have been well established as important influences on the cellular toxin quota [40,116,117]. With the information collected for this study and without an additional genomic investigation [118], we could not evaluate which cyanobacteria were producing the neurotoxins in Chautauqua Lake.…”

Temperature elevation reduces the sensitivity of invasive cladoceran Daphnia lumholtzi to filamentous cyanobacterium Raphidiopsis raciborskii

“…This result indicates that where this exotic filamentous cyanobacterium has successfully invaded aquatic ecosystems in Europe, it may provide an effective obstacle for invasion by D. lumholtzi at sub‐optimal temperatures for this species. Because some strains of R. raciborskii can sustain stable populations at a very low temperature, even 11°C (Bonilla et al, ), and at a wide spectrum of light intensity (10–500 μmol of photons m –2 s –1 , Mesquita, Lürling, Dorr, Pinto, & Marinho, ), it may hinder invasion by D. lumholtzi in spring or late‐autumn. Moreover, cooler water can trigger morphological (increase of filaments length, Rangel et al, ) and physiological (increased saxitoxin production, Mesquita et al, ) alterations in some strains of this cyanobacterium, which might additionally hamper the performance of daphnids.…”