A developmentally regulated gvpABC operon is involved in the formation of gas vesicles in the cyanobacterium Calothrix 7601

In the filamentous cyanobacterium Calothrix PCC7601, gas-vesicle (GV) formation is restricted to specialized filaments, called hormogonia. The differentiation of these cells is controlled by environmental factors, such as light intensity and/or wavelength. The structural gene (gvpA) encoding a GV protein in this cyanobacterium has been previously cloned and sequenced. Two other genes, gvpB and gvpC have been found in the sequence downstream from gvpA. The gvpB gene corresponds to a second copy of gvpA, encoding an identical protein. Unlike the GV protein, the product of the gvpC gene is predominantly hydrophilic, as deduced from nucleotide sequence. Interestingly, the internal part of the gvpC gene is composed of four contiguous repeats, each containing 99 bp, forming highly homologous repeats in the deduced amino acid sequence. Another kind of periodicity has been detected inside the 99-bp repeats, suggesting that the gvpC gene might have evolved by amplification of a 33-bp-long primordial building block. The function of this gene remains to be elucidated. Finally, we have shown that the three genes, gvpA, gvpB, and gvpC, are organized in an operon that is exclusively expressed during GV formation in hormogonia.     

Characterization of two insertion sequences, IS701 and IS702, from the cyanobacterium Calothrix species PCC 7601

We describe the characterization of two insertion elements, IS701 and IS702, isolated from Calothrix species PCC 7601. These insertion elements were cloned from spontaneous pigmentation mutants. Both show the characteristics of typical bacterial insertion sequences, i.e. they present long terminal inverted repeats and they duplicate target DNA upon insertion. These elements share no homology with the only other cyanobacterial insertion sequence described so far, IS891. At least 15 copies of IS701 and 9 copies of IS702 were detected by hybridization experiments in the Calothrix 7601 genome. Their occurrence in several cyanobacterial strains is also reported.     

The amino-acid sequence of three proteins of photosystem I of the cyanobacterium Fremyella diplosiphon (Calothrix sp PCC 7601)

Three proteins containing 138 amino acids (psaD protein), 80 amino acids (psaC protein) and 66 amino acids (psaE protein) of the photosystem I (PS I) complex of the cyanobacterium Fremyella diplosiphon (Calothrix sp PCC 7601) were isolated and sequenced. Comparison with previously known sequences showed a close relationship to homologous proteins of Nostoc, another filamentous cyanobacterium.     

Molecular cloning and nucleotide sequence of a developmentally regulated gene from the cyanobacterium Calothrix PCC 7601: a gas vesicle protein gene.

Since the gas vesicle protein (GVP) is highly conserved among the different gas-vacuolate prokaryotes, a 29-mer oligonucleotide corresponding to a portion of the Anabaena flos-aquae GVP gene was synthesized and used to isolate the GVP structural gene from Calothrix PCC 7601 (= Fremyella diplosiphon). Gas vacuole production in this filamentous cyanobacterium is restricted to hormogonia which occur at a specific stage during the developmental cell cycle. The GVP gene (gvpA) was localized on a 709 bp HindIII-HincII fragment. Nucleotide sequence analysis revealed a 213 bp open reading frame whose deduced amino-acid sequence shows a very high homology with that of the Anabaena flos-aquae GVP. Assuming that the first methionine residue is proteolytically processed, the molecular mass of the Calothrix GVP is 7375 daltons. Sequences resembling the Escherichia coli consensus promoter were found upstream from the gvpA gene. The initiator codon of the gvpA gene is preceded by a polypurine sequence assumed to be the ribosome binding site. Southern hybridizations with a probe specific for the gvpA gene indicated that this gene is not plasmid-borne, and that another homologous gene is present in the Calothrix genome.     

A phycourobilin-containing phycoerythrin from the cyanobacterium Oscillatoria sp.

A filamentous cyanobacterium Oscillatoria sp. was isolated from a thermal spring of the Kamchatka peninsula. It contained a phycoerythrin unusual for cyanobacteria in that it had a phycourobilin prosthetic group. The absorption spectrum of the native purified phycoerythrin displayed maxima at 498 and 567 nm. The phycoerythrin comprised - and -subunits of molecular weights 18,700 and 19,800, respectively, in 1:1 stoichiometry. Polyacrylamide gel isoelectric focusing revealed one protein band at pI 4.6. The - and -subunits differed in their chromophore composition and content: -subunit carried two phycoerythrobilins while the -subunit had three phycoerythrobilins and one phycourobilin. The chromophore composition of all known phycoerythrins of cyanobacteria and red algae were compared, and on the basis of this comparative study designations C₁- to C₅-phycoerythrin were proposed for cyanobacterial red pigments.     

Three C-phycoerythrin-associated linker polypeptides in the phycobilisome of green-light-grown Calothrix sp. PCC 7601 (cyanobacteria).

Microanalyses by SDS-PAGE and microsequencing demonstrate that, under green-light conditions, 3 C-phycoerythrin associated rod-linker polypeptides with different N-terminal amino acid sequences are present in phycobilisomes (PBS) from Calothrix sp. 7601 cells. Two of these polypeptides, corresponding to SDS-PAGE bands at 36 and 37 kDa, could be assigned, respectively, to the cpeC and cpcD genes found on a separate cpeCD-operon in Calothrix sp. 7601 (Federspiel, N.A. and Grossman, A.R. (1990) J. Bacteriol, 172, 4072-4081). The third C-PE rod-linker polypeptide, LR,2PE,33, requires, therefore, a third gene with the suggested locus designation 'cpeE'. A C-PE (alpha beta)6-LR,2PE,33 complex containing this third rod-linker polypeptide could be isolated from phycobilisomes and characterized. PBS from both green- and red-light cells of Calothrix contain a single, unique LRC28 rod-core linker polypeptide which is not altered during chromatic adaptation.     

Phosphomonoesterase activity of the cyanobacterium (blue-green alga) Calothrix parietina

Cellular and extracellular phosphomonoesterase activities were compared in Calothrix parietina D550, a strain whose original environment has been studied in detail. Activity in both fractions became detectable at about the same stage in batch culture. Differences in the influence of environmental factors between the two were slight, suggesting a common origin. The optimum temperatures for cellular and extracellular activities were 40 degrees C and 30 degrees C, respectively, and the upper limits for detectable activity were 80 degrees C and 65 degrees C. The pH optimum for both cellular and extracellular activity was 10.0-10.2. When P-limited cultures were tested with p-nitrophenyl phosphate (pNPP) as substrate, Km values for cellular and extracellular activities were 43 and 33 microM pNPP, respectively. Eleven ions were tested for their influence on activity. In most cases the effect was low or negligible at concentrations likely to be present in nature or freshwater laboratory media. Where obvious effects occurred, these were usually apparent at lower concentrations with extracellular than cellular activity. One mM Ca led to a 40% increase in extracellular activity in comparison with 0.1 mM Ca, but had no effect on cellular activity. However, inorganic phosphate, which had a marked inhibitory effect at concentrations above 10 microM, brought about a similar response with cellular and extracellular activities (approximately 60% decrease with 100 microM).