Abstract
Cyanobacteria are major bloom-forming organisms in freshwater ecosystems and many strains are known to produce toxins. Toxin production requires an investment in energy and resources. As light is one of the most important factors for cyanobacterial growth, any changes in light climate might affect cyanobacterial toxin production as well as their growth and physiology. To evaluate the effects of light on the growth and physiological parameters of both toxic and non-toxic strains of Microcystis aeruginosa and Anabaena circinalis, cultures were grown at a range of light intensities (10, 25, 50, 100, 150 and 200 µmol m−2 s−1). The study revealed that the toxic strains of both species (CS558 for M. aeruginosa and CS537 and CS541 for A. circinalis) showed growth (µ) saturation at a higher light intensity compared to the non-toxic strains (CS338 for M. aeruginosa and CS534 for A. circinalis). Both species showed differences in chlorophyll a, carotenoid, allophycocyanin (APC) and phycoerythrin (PE) content between strains. There were also differences in dark respiration (Rd), light saturated oxygen evolution rates (Pmax) and efficiency of light harvesting (α) between strains. All other physiological parameters showed no statistically significant differences between strains. This study suggest that the different strains respond differently to different light habitats. Thus, changes in light availability may affect bloom intensity of toxic and nontoxic strains of cyanobacteria by changing the dominance and succession patterns.
Highlights
Cyanobacteria play significant roles in the nitrogen, carbon and oxygen dynamics of many aquatic ecosystems
A number of factors are responsible for the expansion of harmful cyanobacterial blooms including nutrient enrichment, often associated with agricultural activity, and increased surface water temperature due to global climate change [5,6,7]
Several genera of cyanobacteria are responsible for potent toxin production, of which most are bloom forming
Summary
Cyanobacteria play significant roles in the nitrogen, carbon and oxygen dynamics of many aquatic ecosystems They are major bloom-forming organisms in freshwater ecosystems all over the world and blooms cost millions of dollars annually in lost income and amenities [1]. According to Connolly et al [2], the predicted cost of nutrient-induced cyanobacterial blooms in just a single system in Australia, the Gippsland Lakes of Victoria, has been estimated to be $256 million over the 20 years These economic costs are predicted to increase over time, due to a warming climate increasing the incidence of algal blooms [3,4]. In this paper we present the results of investigations of growth and physiological characteristics of both toxic and non-toxic strains of the cyanobacteria Anabaena circinalis and Microcystis aeruginosa in relation to light environment
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