Genetic engineering of the unsaturation of fatty acids in membrane lipids alters the tolerance ofSynechocystisto salt stress

Abstract

The role of unsaturated fatty acids in membrane lipids in the tolerance of the photosynthetic machinery to salt stress was studied by comparing the desA ؊ ͞desD ؊ mutant of Synechocystis sp. PCC 6803, which contained monounsaturated fatty acids, with the wild-type strain, which contained a full complement of polyunsaturated fatty acids. In darkness, the loss of oxygen-evolving photosystem II activity in the presence of 0.5 M NaCl or 0.5 M LiCl was much more rapid in desA ؊ ͞desD ؊ cells than in wild-type cells. Oxygenevolving activity that had been lost during incubation with 0.5 M NaCl in darkness returned when cells were transferred to conditions that allowed photosynthesis or respiration. Recovery was much greater in wild-type than in desA ؊ ͞desD ؊ cells, and it was prevented by lincomycin. Thus, the unsaturation of fatty acids is important in the tolerance of the photosynthetic machinery to salt stress. It appears also that the activity and synthesis of the Na ؉ ͞H ؉ antiporter system might be suppressed under high-salt conditions and that this effect can be reversed, in part, by the unsaturation of fatty acids in membrane lipids.The regulation of the unsaturation of fatty acids in membrane lipids is important in the acclimation of poikilothermic organisms to changing environmental conditions, in particular, temperature (1-4). The effects of temperature on the desaturation of fatty acids have been extensively studied in cyanobacteria (for reviews, see refs. 2 and 5). When the ambient temperature is shifted from high to low, cyanobacterial cells synthesize fatty acid desaturases that introduce double bonds into the fatty acids of membrane lipids.In a previous study we isolated a desA Ϫ ͞desD Ϫ mutant strain of the cyanobacterium Synechocystis sp. PCC 6803 in which the desA and desD genes for the ⌬12 and ⌬6 desaturases, respectively, had been inactivated by targeted mutagenesis (6). The desA Ϫ ͞desD Ϫ cells contain monounsaturated but not polyunsaturated fatty acids, whereas wild-type cells contain polyunsaturated fatty acids such as di-, tri-, and tetraunsaturated fatty acids (7). By comparing these two strains we found that polyunsaturated fatty acids are essential for growth in Synechocystis sp. PCC 6803 at low temperatures (6).In the present study, we investigated the contribution of the unsaturation of fatty acids in membrane lipids to tolerance to salt stress by comparing desA Ϫ ͞desD Ϫ cells to wild-type cells of Synechocystis sp. PCC 6803. We demonstrated that the unsaturation of fatty acids is associated with the ability of the photosynthetic machinery to tolerate salt stress. MATERIALS AND METHODS Cells, Culture Conditions, and Preparation of ThylakoidMembranes. Wild-type and desA Ϫ ͞desD Ϫ (6) cells of Synechocystis sp. PCC 6803 were grown photoautotrophically in BG-11 medium (pH 7.5) (23), which contained 20 mM Na ϩ ions at 35°C under constant illumination from incandescent lamps (70-80 E⅐m Ϫ2 ⅐s Ϫ1, in which E indicates an einstein, 1 mol of photons) with aeration by sterile air that cont...

Overexpression of a Na + /H + antiporter confers salt tolerance on a freshwater cyanobacterium, making it capable of growth in sea water

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α-Tocopherol Plays a Role in Photosynthesis and Macronutrient Homeostasis of the Cyanobacterium Synechocystis sp. PCC 6803 That Is Independent of Its Antioxidant Function

“…Light-dependent inactivation of photosynthesis, termed photoinhibition, is often observed under a variety of environmental stresses, including high-intensity light (Allakhverdiev et al, 1999;Hideg et al, 2000;Trebst et al, 2002; for review, see Aro et al, 1993, and refs. therein).…”

The Structure and Gene Repertoire of an Ancient Red Algal Plastid Genome

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