Robust photosystem I activity by Cyanothece sp. (Cyanobacteria) and its role in prolonged bloom persistence in lake St Lucia,South Africa |
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Authors: | du Plooy Schalk J Anandraj Akash White Sarah Perissinotto Renzo du Preez Derek R |
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Institution: | 1.DST/NRF Research Chair in Shallow Water Ecosystems, Nelson Mandela University, PO Box 77000, Port Elizabeth, 6031, South Africa ;2.Center for Algal Biotechnology, Mangosuthu University of Technology, Jacobs, P.O. Box 12363, Durban, 4026, South Africa ;3.Botany Department, Nelson Mandela University, PO Box 77000, Port Elizabeth, 6031, South Africa ; |
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Abstract: | Worldwide, cyanobacterial blooms are becoming more frequent, exacerbated by eutrophication, anthropogenic effects, and global climate change. Environmental factors play a direct role in photosynthesis of cyanobacteria and subsequent cellular changes, growth, and bloom dynamics. This study investigated the photosynthetic functioning of a persistent bloom-forming (18 months) cyanobacterium, Cyanothece sp., isolated from Lake St Lucia, South Africa. DUAL-PAM fluorometric methods were used to observe physiological responses in Cyanothece sp. photosystems I and II. Results show that photosystem I activity was maintained under all environmental conditions tested, while photosystem II activity was not observed at all. Out of the environmental factors tested (temperature, salinity, and nitrogen presence), only temperature significantly influenced photosystem I activity. In particular, high temperature (40 °C) facilitated faster electron transport rates, while effects of salinity and nitrogen were variable. Cyanothece sp. has shown to sustain bloom status for long periods largely because of the essential role of photosystem I activity during highly dynamic and even extreme (e.g., salinities higher than 200) environmental conditions. This ensures the continual supply of cellular energy (e.g. ATP) to important processes such as nitrogen assimilation, which is essential for protein synthesis, cell growth and, therefore, bloom maintenance. |
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