Interrelation between cyanophycin synthesis, L-arginine catabolism and photosynthesis in the cyanobacterium Synechocystis sp strain PCC 6803

Ultrastructural and immunocytochemical investigations gave evidence that cy anophycin (multi-L-arginyl-poly-L-aspartate) granules accumulate in the cya nobacterium Synechocystis sp. strain PCC 6803 under nutrient deficient grow th conditions, especially under phosphate limitation. Besides nutrient defi ciency, growth of Synechocystis PCC 6803 on L-arginine or L-asparagine as s ole N-source also led to high increase of cyanophycin synthesis, while grow th on the combination of L-arginine or L-asparagine with nitrate only cause d minor cyanophycin accumulation. Growth of Synechocystis PCC 6503 on L-arg inine as sole N-source caused substantial morphological and physiological c hanges, such as severe thylakoid membrane degradation with partial loss of pigments and photosynthetic activity leading to a phenotype almost like tha t seen under nutrient deficiency. In contrast to the wild type, the PsbO-fr ee Synechocystis PCC 6803 mutant could grow on L-arginine as sole N-source with only minor morphological and physiological changes. Due to its fairly balanced growth, the mutant accumulated only few cyanophycin granules. L-ar ginine degrading activity (measured as ornithine and ammonium formation) wa s high in the PsbO-free mutant but not in the wild type when cells were gro wn on L-arginine as sole N-source. In both cells types the L-arginine degra ding activity was high (although in the PsbO-free mutant about twice as hig h as in wild type), when cells were grown on L-arginine in combination with nitrate, and as expected very low when cells were grown on nitrate as sole N-source. Thus, net cyanophycin accumulation in Synechocystis PCC 6803 is regulated by the relative concentration of L-arginine to the total nitrogen pool, and the intracellular L-arginine concentration is greatly influenced by the activity of the L-arginine degrading enzyme system which in part is regulated by the activity status of photosystem II. These results suggest a complex interrelation between cyanophycin synthesis, L-arginine catabolis m, and in addition photosynthesis in Synechocystis PCC 6803.