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 degrees C) and irradiances (15-340 mu E m(-2) s(-1)). This species grew in temperatures ranging from 15 degrees C to 35 degrees 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 degrees C and at 60 mu E m(-2) s(-1). CYN was produced under all conditions where net growth occurred. Total CYN reached up to 6.4 mu g mg(-1) dry weight, 2.4 mu g mm(-3) biovolume, 190.6 fg cell(-1) and 0.5 mu g mu g(-1) chlorophyll a. Although CYN concentrations varied only 1.9-fold within the 15-30 degrees C range, a drastic 25-fold decrease was observed at 35 degrees C. The irradiance induced up to 4-fold variations, with maximum total CYN measured at 60 mu E m(-2) s(-1). An elevated extracellular CYN share ranging from 20% to 35% was observed during the exponential growl:h phase in most experiments, with extreme temperatures (15 and 35 degrees 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. (C) 2011 Elsevier B.V. All rights reserved.