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Photosynthetic adaptation to light availability shapes the ecological success of bloom-forming cyanobacterium Pseudanabaena to iron limitation
Authors:Zheng-Ke Li  Guo-Zheng Dai  Yong Zhang  Kui Xu  Laura Bretherton  Zoe V Finkel  Andrew J Irwin  Philippe Juneau  Bao-Sheng Qiu
Institution:1. School of Life Sciences, and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, Hubei, 430079 People’s Republic of China;2. College of Environmental Science and Engineering, Fujian Normal University, Fuzhou, Fujian, 350007 People’s Republic of China;3. School of Environmental Science and Engineering, Environmental Microbiomics Research Center, Sun Yat-Sen University, Guangzhou, Guangdong, 510006 People’s Republic of China;4. Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3H 4R2 Canada;5. Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia, B3H 4R2 Canada;6. Ecotoxicology of Aquatic Microorganisms Laboratory – Department of Biological Sciences, GRIL - EcotoQ - TOXEN, Université du Québec à Montréal, Succ. Centre-Ville, Montréal, Québec, H3C 3P8 Canada
Abstract:The poorly understood filamentous cyanobacterium Pseudanabaena is commonly epiphytic on Microcystis colonies and their abundances are often highly correlated during blooms. The response and adaptation of Microcystis to iron limitation have been extensively studied, but the strategies Pseudanabaena uses to respond to iron limitation are largely unknown. Here, physiological responses to iron limitation were compared between one Pseudanabaena and two Microcystis strains grown under different light intensities. The results showed that low-intensity light exacerbated, but high-intensity light alleviated, the negative effect of iron limitation on Pseudanabaena growth relative to two Microcystis strains. It was found that robust light-harvesting and photosynthetic efficiency allowed adaptation of Pseudanabaena to low light availability relative to two Microcystis strains only during iron sufficiency. The results also indicated that a larger investment in the photosynthetic antenna probably contributed to light/iron co-limitation of Pseudanabaena relative to two Microcystis strains under both light and iron limitation. Furthermore, the lower antenna pigments/chlorophyll a ratio and photosynthetic efficiency, and higher nonphotochemical quenching and saturation irradiance provided Pseudanabaena photoadaptation and photoprotection advantages over the two Microcystis strains under the high-light condition. The lower investment in antenna pigments of Pseudanabaena than the two Microcystis strains under high-light intensity is likely an efficient strategy for both saving iron quotas and decreasing photosensitivity. Therefore, when compared with Microcystis, the high plasticity of antenna pigments, along with the excellent photoadaptation and photoprotection ability of Pseudanabaena, probably ensures its ecological success under iron limitation when light is sufficient.
Keywords:blooms  iron limitation  light  Microcystis  photosynthesis  Pseudanabaena
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