Cylindrospermopsin production and release by the potentially invasive cyanobacterium Aphanizomenon ovalisporum under temperature and light gradients

The growth rates, production and release of the potent cytotoxin cylindrospermopsin (CYN) were studied in batch and semi-continuous cultures of Aphanizomenon ovalisporum (Cyanobacteria; Nostocaceae) strains UAM 289 and UAM 290 from Spain, over a gradient of temperatures (10–40 °C) and irradiances (15–340 μE m−2 s−1). This species grew in temperatures ranging from 15 °C to 35 °C as well as under all irradiances assayed. The growth rates ranged from 0.08 d−1 to 0.35 d−1, and the maximum growth was recorded above 30 °C and at 60 μE m−2 s−1. CYN was produced under all conditions where net growth occurred. Total CYN reached up to 6.4 μg mg−1 dry weight, 2.4 μg mm−3 biovolume, 190.6 fg cell−1 and 0.5 μg μg−1 chlorophyll a. Although CYN concentrations varied only 1.9-fold within the 15–30 °C range, a drastic 25-fold decrease was observed at 35 °C. The irradiance induced up to 4-fold variations, with maximum total CYN measured at 60 μE m−2 s−1. An elevated extracellular CYN share ranging from 20% to 35% was observed during the exponential growth phase in most experiments, with extreme temperatures (15 and 35 °C) being related to the highest release (63% and 58%, respectively) and without remarkable influence of irradiance. Growth did not have a direct influence on either CYN production or release throughout the entire range of experimental conditions. Our study demonstrates a strong and stable production and release of CYN by A. ovalisporum along field-realistic gradients of temperature and light, thus becoming a predictive tool useful for the management of water bodies potentially affected by this ecologically plastic cyanobacterium.

► CYN was produced by A. ovalisporum under 15–35 °C and 15–340 μE m−2 s−1.
► CYN content reached 6 μg mg−1 dry weight, varying up to 4-fold due to light shifts.
► CYN content varied only 2-fold within 15–30 °C range and decreased 25-fold at 35 °C.
► Extracellular CYN represented 20–63% of total CYN.
► Extracellular CYN above 50% coincided with extreme temperatures and/or growth rates.