On the functional significance of the polypeptide PsbY for photosynthetic water oxidation in the cyanobacterium Synechocystis sp. strain PCC 6803.

Recent investigations have revealed that the cyanobacterial photosystem II complex contains more than 26 polypeptides. The functions of most of the low-molecular-mass polypeptides, including PsbY, have remained elusive. Here we present a comparative characterization of the wild-type Synechocystis sp. strain PCC 6803 and a PsbY-free mutant derived from it. The results show that growth of the PsbY-free mutant was comparable to that of the wild-type when cells were cultivated in complete BG11 medium or under initial manganese or chloride limitation, and when illuminated at 20 or 200 microE m(-2) s(-1). However, while growth rates of both the wild-type and the PsbY-free mutant were reduced when cells were cultivated in BG11 medium in the absence of calcium, the reduction was significantly greater in the case of the PsbY-free mutant. This differential effect on growth of the mutant relative to the wild-type in CaCl(2) deficient medium was detected when the cells were illuminated with high-intensity light (200 microE m(-2) s(-1)) but not when light levels were lower (20 microE m(-2) s(-1)). The differential effect on growth was associated with lower O(2) evolving activity in the mutant compared to wild-type cells. The mutant was also found to be more sensitive to photoinhibition, and showed an altered pattern of fluorescence emission at 77 K. In addition, mass spectrometric analysis revealed that PsbY-free cells cultivated in CaCl(2) sufficient medium (in which no growth reduction was observed) had a significantly higher O(2) evolution from hydrogen peroxide and a lower O(2) evolution from water under flash light illumination than wild-type cells. These results imply that photosystem II is slightly impaired in the PsbY-free mutant, and that the mutant is less capable of coping with low levels of Ca(2+) than the wild-type.

A mutant of the cyanobacterium Anabaena variabilis ATCC 29413 lacking cyanophycin synthetase: growth properties and ultrastructural aspects.

The gene cphA encoding cyanophycin synthetase was interrupted in Anabaena variabilis ATCC 29413 by insertional mutagenesis. The mutant lacked cyanophycin granules and the polar nodules of heterocysts. The mutant grew as fast as the wild-type irrespective of the nitrogen source at low light intensity whereas growth on N(2) was somewhat reduced in high light. It is concluded that cyanophycin metabolism and polar nodules are not essential for aerobic N(2) fixation.

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

Ultrastructural and immunocytochemical investigations gave evidence that cyanophycin (multi-L-arginyl-poly-L-aspartate) granules accumulate in the cyanobacterium Synechocystis sp. strain PCC 6803 under nutrient deficient growth conditions, especially under phosphate limitation. Besides nutrient deficiency, growth of Synechocystis PCC 6803 on L-arginine or L-asparagine as sole N-source also led to high increase of cyanophycin synthesis, while growth on the combination of L-arginine or L-asparagine with nitrate only caused minor cyanophycin accumulation. Growth of Synechocystis PCC 6803 on L-arginine as sole N-source caused substantial morphological and physiological changes, such as severe thylakoid membrane degradation with partial loss of pigments and photosynthetic activity leading to a phenotype almost like that seen under nutrient deficiency. In contrast to the wild type, the PsbO-free 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-arginine degrading activity (measured as ornithine and ammonium formation) was high in the PsbO-free mutant but not in the wild type when cells were grown on L-arginine as sole N-source. In both cells types the L-arginine degrading activity was high (although in the PsbO-free mutant about twice as high 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 catabolism, and in addition photosynthesis in Synechocystis PCC 6803.