Growth at low temperature causes nitrogen limitation in the cyanobacterium Synechococcus sp. PCC 7002
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© Springer-Verlag 1998
O R I G I N A L PA P E R
Toshio Sakamoto · Donald A. Bryant
Growth at low temperature causes nitrogen limitation in the cyanobacterium Synechococcus sp. PCC 7002
Received: 24 April 1997 / Accepted: 5 August 1997
Abstract The coloration of cells of the cyanobacterium Synechococcus sp. PCC 7002 changed from normal bluegreen to yellow-green when cells were grown at 15° C in a medium containing nitrate as the sole nitrogen source. This change of coloration was similar to a general response to nutrient deprivation (chlorosis). For the chlorotic cells at 15° C, the total amounts of phycobiliproteins and chlorophyll a decreased, high levels of glycogen accumulated, and growth was arithmetic rather than exponential. These changes in composition and growth occurred in cells grown at low (50 µE m–2 s–1) as well as high (250 µE m–2 s–1) light intensity. After a temperature shift-up to 38° C, chlorotic cells rapidly regained their normal blue-green coloration and normal exponential growth rate within 7 h. When cells were grown at 15° C in a medium containing urea as the reduced nitrogen source, cells grew exponentially and the symptoms of chlorosis were not observed. The decrease in photosynthetic oxygen evolution activity at low temperature was much smaller than the decrease in growth rate for cells grown on nitrate as the nitrogen source. These studies demonstrate that low-temperature-induced chlorosis of Synechococcus sp. PCC 7002 is caused by nitrogen limitation and is not the result of limited photosynthetic activity or photodamage to the photosynthetic apparatus, and that nitrogen assimilation is an important aspect of the low-temperature physiology of cyanobacteria. Key words Chilling tolerance · Chlorosis · Cyanobacterium · Low-temperature acclimation · Nitrogen assimilation · Phycobiliprotein
T. Sakamoto · D. A. Bryant (Y) Department of Biochemistry and Molecular Biology, S-234 Frear Building, The Pennsylvania State University, University Park, PA 16802, USA Tel. +1 814-865-1992; Fax +1 814-863-7024 e-mail: [email protected]
Abbreviations Chl a Chlorophyll a · PCC Pasteur Culture Collection · PS I photosystem I · PS II photosystem II
Introduction Cyanobacteria are the largest, most structurally diverse, and most widely distributed group of phototrophic eubacteria (Stanier and Cohen-Bazire 1977). Their simple nutritional requirements – light, water, carbon dioxide, and inorganic salts – allow these organisms to occupy highly diverse ecological niches. Psychrophilic and thermophilic cyanobacteria have been identified, and examples of organisms that can grow at temperatures ranging from approximately 0 to 75° C are known (Castenholtz 1969; Fogg et al. 1973). Although the temperature range over which cyanobacteria can grow is quite large, for any given organism the temperature range over which growth can occur is typically more narrow and rarely exceeds a span of 30 to 40° C, as is commonly observed for other bacteria. Since ambient growth temperature is a fundamental physical parameter that can f
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