Photosynthetic characteristics of two Cylindrospermopsis raciborskii strains differing in their toxicity

Abstract

We studied the growth and photosynthetic characteristics of a toxic (CS506) and a nontoxic strain (CS509) of the bloom-forming cyanobacterium Cylindrospermopsis raciborskii grown under identical experimental conditions. When exposed to light-saturating growth conditions (100 μmol photons · m(-2) · s(-1) ), values for maximal photosynthetic capacity (Pmax ) and maximum quantum yield (Fv /Fm ) indicated that both strains had an equal ability to process captured photons and deliver them to PSII reaction centers. However, CS506 grew faster than CS509. This was consistent with its higher light requirement for saturation of photosynthesis (Ik ). Greater shade tolerance of CS509 was indicated by its higher ability to harvest light (α), lower photosynthetic light compensation point (Ic ), and higher chlorophyll a to biovolume ratio. Strain-specific differences were found in relation to non-photochemical quenching, effective absorption cross-sectional area of PSIIα-centers (σPSIIα), and the antenna connectivity parameter of PSIIα (Jcon PSIIα). These findings highlighted differences in the transfer of excitation from phycobilisome/PSII to PSI, on the dependence on different pigments for light harvesting and on the functioning of the PSII reaction centers between the two strains. The results of this study showed that both performance and composition of the photosynthetic apparatus are different between these strains, though with only two strains examined we cannot attribute the performance of strain 506 to its ability to produce cylindrospermopsins. The emphasis on a strain-specific light adaptation/acclimation is crucial to our understanding of how different light conditions (both quantity and quality) can trigger the occurrence of different C. raciborskii strains and control their competition and/or dominance in natural ecosystems.

Constitutive Cylindrospermopsin Pool Size in Cylindrospermopsis raciborskii under Different Light and CO 2 Partial Pressure Conditions

“…Culture growth was measured spectrophotometrically at 750 nm, while cell concentration was measured microscopically (33). During log phase, there was a linear correlation between the optical density at 750 nm (OD 750 ) and cell concentration over the range of cell concentrations measured (r 2 Ͼ 0.98).…”

“…To investigate the effects of light regimen on growth, CYN pool size, and gene expression, cultures were grown under subsaturating (10 mol photons [photosynthetically active radiation, or PAR] m Ϫ2 s Ϫ1 ) and potentially saturating (100 mol photons [PAR] m Ϫ2 s Ϫ1 ) light intensities. A previous study had shown that the cell division rate ( c ) was saturating at the higher light level and was subsaturating at the lower level (33). Cultures were preacclimated under the experimental conditions for at least 15 days prior to the experiment.…”

“…Previous studies by Pierangelini et al (33,34) showed that the specific cell division rate ( c ) of C. raciborskii CS506 varied under different light intensities and CO 2 levels. To expand our knowledge about the effects of environmental parameters on the intracellular CYN pool size of C. raciborskii (strain CS506), we investigated how different light and CO 2 regimens regulated the expression of genes involved in CYN biosynthesis, such as cyrA (amidinotransferase, the first step in CYN biosynthesis) and cyrK (putative transport), and the impact these factors have on (i) the rate of production, (ii) CYN cell quotas for CYN (Q CYN ) and dCYN (Q dCYN ), and (iii) the extracellular volumetric concentrations of CYN and dCYN.…”

Morpho-physiological responses of a subtropical strain of Cylindrospermopsis raciborskii (Cyanobacteria) to different light intensities

“…Historically, Padisák & Reynolds (1998) considered C. raciborskii a cyanobacterium adapted to grow under low light intensities. Later, more research in the field and using strains from different water bodies has pointed out C. raciborskii grows in a wide range of light intensity (Saker et al 1999;O'brien et al 2009;Bittencourt-Oliveira et al 2011;Pierangelini et al 2014), while the light requirements for growth were low (I k near to 20 μmol photons m -2 s -1…”

The success of the cyanobacterium Cylindrospermopsis raciborskii in freshwaters is enhanced by the combined effects of light intensity and temperature

“…Since the original classification of C. raciborskii as a shade-tolerant species (Padisák and Reynolds, 1998) with low saturation light intensities for growth (I k <26 µmol photon m -2 s -1 ) (Briand et al, 2004), new evidence has shown that this species has a high phenotypic plasticity that may explain its good performance at high light intensities (Saker and Eaglesham, 1999;Piccini et al, 2011;Bonilla et al, 2012;Pierangelini et al, 2014). Thus, light intensity itself may be not sufficient to explain the expansion of C. raciborskii, since it was reported to tolerate both low and high light intensities in temperate (Dokulil and Teubner, 2000;Wiedner et al, 2007) and tropical regions (Soares et al, 2009;Gomes et al, 2013).…”