Detection of a homologue to an E. coli glutamate synthase gene in a cyanobacterium

The gltBY locus of E. coli, which codes for the two subunits of pyridine nucleotide dependent glutamate synthase, was used as a probe to detect homologues in genomic DNA of Synechococcus PCC6301, a unicellular cyanobacterium. Non-overlapping probes from gltB detected a single homologue with extensive homology, however gltY probes do not detect a strong homologue. The possibility that the gltB homologue encodes a ferredoxin-dependent glutamate synthase of the type found in cyanobacteria, algae and plants is discussed.     

Electrogenicity at the donor/acceptor sides of cyanobacterial photosystem I

To study electrogenesis the photosystem I particles fromSynechococcus elongatus were incorporated into asolectin liposomes, and fast kinetics of laser flash-induced electric potential difference generation has been measured by a direct electrometric method in proteoliposomes adsorbed on a phospholipid-impregnated collodion film. The photoelectric response has been found to involve three electrogenic stages associated with (i) iron-sulfur center F_x reduction by the primary electron donor P700, (ii) electron transfer between iron-sulfur centers F_x and F_A/F_B, and (iii) reduction of photo-oxidized P700⁺ by reduced cytochromec ₅₅₃. The relative magnitudes of phases (ii) and (iii) comprised about 20% of phase (i).     

Phenotype variability of identical genotypes: the need for a combined approach in cyanobacterial taxonomy demonstrated on Merismopedia-like isolates

Five Merismopedia-like cyanobacterial strains were collected from microbial mats at Norderney Island, subcultured in the laboratory, and finally grown as unicyanobacterial cultures. As a sixth strain, Merismopedia glauca from the ?Sammlung von Algenkulturen“ at Göttingen (SAG) was used for comparisons. According to morphological and physiological characteristics initially observed in the field and during initial subculturing, the five strains were assigned to the species Merismopedia glauca, Merismopedia punctata, or Merismopedia elegans. However, after prolonged maintenance under laboratory conditions, the formation of platelet-like colonies stopped, whereas cell sizes, production of extracellular polymeric substances, and division patterns were stably maintained. These physiological and morphological parameters allowed us to divide the six strains into two clusters. This division was further supported by the profiling of total cell protein and phycobilisomes using SDS-PAGE. The nearly complete 16S rDNA sequence of three of the six isolates was determined. The comparative sequencing analysis revealed an almost 100% identity of these three Merismopedia-like strains. The evolutionary distance dendrogram constructed placed this Merismopedia cluster into a common line of descent with Synechocystis sp. strain PCC6906. Based on the analysis of common stretches of 1,050 nucleotides, the overall similarity between the sequence types of ?Merismopedia“ and ?Synechocystis“ is 96–97%. The values of the different methods for taxonomic classification of unicyanobacterial strains, the relationship of the cyanobacterial genera Merismopedia, Synechococcus, Synechocystis, and Eucapsis sp., and the functional role of different Merismopedia morphologies within microbial mats are discussed. It is suggested that all analyzed Merismopedia strains be combined into one species, namely Merismopedia punctata Meyen (1839).     

A photoactive Photosystem-II reaction-center complex lacking a chlorophyll-binding 40 kilodalton subunit from the thermophilic cyanobacterium Synechococcus sp.

The Photosystem-II reaction-center complex of the thermophilic cyanobacterium Synechococcus sp. was resolved into two complemental chlorophyll-protein complexes, CP2b which contained a chlorophyll-binding 47 kDa polypeptide, two polypeptides in the 28–31 kDa region and a 9 kDa polypeptide, and CP2c which had only a chlorophyll-binding 40 kDa polypeptide. CP2b was found to be highly active in photoreduction of 2,6-dichlorophenolindophenol with diphenylcarbazide as an electron donor. The activity was insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea and ioxynil but was half inactivated by the treatment of the complex at 50°C for 5 min, or on addition of 0.001% sodium dodecyl sulfate, indicating its dependence on the protein conformation. CP2c also showed a low activity of the dye photoreduction, which was insensitive to heat and enhanced at high concentrations of sodium dodecyl sulfate. The quantum yield of the photoreduction was estimated to be 0.12 for CP2b and 0.002 for CP2c. It is concluded that the 47 kDa polypeptide is the site of the Photosystem-II reaction center and the 40 kDa polypeptide is not required for the Photosystem-II-driven electron transport.