The gas vesicle gene (gvp) cluster of the cyanobacterium Pseudanabaena sp. strain PCC 6901.

A gene cluster located downstream from gvpA in the cyanobacterium Pseudanabaena sp. strain PCC 6901 has been cloned and sequenced. The three genes, orf1, gvpN and gvpJ, are consecutive with no intergenic region. In contrast to GvpN and GvpJ, which share high similarity at the amino acid level with their counterparts in other cyanobacteria and halophilic archaea, Orf1 is only 29% identical to the C-terminal part of GvpC from Anabaena flos-aquae and its sequence organization is reminiscent of the halophilic archaeal GvpC.

Characterization of the genes encoding phycoerythrin in the red alga Rhodella violacea: evidence for a splitting of the rpeB gene by an intron.

The phycobilisome of the eukaryotic unicellular red alga Rhodella violacea presents in some respects an organization that is intermediate between those of the homologous counterparts found in cyanobacteria (the putative chloroplast progenitor) and more advanced, pluricellular red algae. This suggests evolutionary relationships that we investigated at the genome level. The present work describes the sequences of two rhodophytan phycobilisome genes, rpeA and rpeB. These chloroplast genes encode the alpha and beta subunits of phycoerythrin, the major component of the light-harvesting antennae and one of the most abundant cellular proteins in these algae. The amino acid sequences deduced from both rpeA and rpeB present strong homologies with those previously reported for phycoerythrin subunits of cyanobacteria, rhodophyta, and cryptomonads. The main difference with the corresponding cyanobacterial genes was the unexpected occurrence of an intervening sequence that split rpeB into two exons. This intervening sequence presents characteristics of group II introns but lacks several structural domains. Transcriptional analyses showed that the two rpe genes are cotranscribed and that the major RNA species detected corresponds to a mature mRNA lacking the intron. As the phycobiliproteins form a group of closely related polypeptides in cyanobacteria and rhodophyta, the molecular events affecting the corresponding genes, such as the rpeB intron, may be a clue to elucidate some aspects of the molecular processes involved in the evolution of plastid genes.

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.

Photosynthetic electron transport controls nitrogen assimilation in cyanobacteria by means of posttranslational modification of the glnB gene product.

A glnB gene is identified in the cyanobacterium Synechococcus sp. PCC 7942, and its gene product is found to be covalently modified as a result of imbalance in electron transfer in photosynthesis, where photosystem II is favored over photosystem I. The gene was cloned and sequenced and found to encode a polypeptide of 112 amino acid residues, whose sequence shows a high degree of similarity to the Escherichia coli regulatory protein, PII. In E. coli, PII is involved in signal transduction in transcriptional and post-translational regulation of nitrogen assimilation. Increase in ammonium ion concentration is shown to decrease covalent modification of the Synechococcus PII protein, as in enteric bacteria. We therefore propose that the photosynthetic electron transport chain may regulate the pathway of nitrogen assimilation in cyanobacteria by means of posttranslational, covalent modification of the glnB gene product. The existence of the glnB gene in different strains of cyanobacteria is demonstrated and its implications are discussed.

Gas vesicle synthesis in the cyanobacterium Pseudanabaena sp.: occurrence of a single photoregulated gene.

Gas vesicles are subcellular inclusions found in a large number of aquatic prokaryotes. The gvpA gene, which frequently occurs as a multigene family, encodes the major gas vesicle structural protein. In several cyanobacteria, another gene, gvpC, encodes a different protein which might be a dispensable element for gas vesicle formation. We report here the molecular characterization of a gvpA gene in Pseudanabaena sp. PCC 6901. In this planktonic cyanobacterium, it is the only gvp gene which could be detected, and electrophoretic analysis of isolated gas vesicles revealed the presence of a single protein. A monocistronic mRNA species corresponds to the transcription of the gvpA gene and the abundance of the gvpA mRNA is inversely correlated with photosynthetic photon flux indicating that a light-dependent transcriptional regulation is likely to be involved in the control of gas vacuolation in this strain.

Highly repetitive DNA sequences in cyanobacterial genomes.

We characterized three distinct families of repeated sequences in the genome of the cyanobacterium Calothrix sp. strain PCC 7601. These repeated sequences were present at a level of about 100 copies per Calothrix genome and consisted of tandemly amplified heptanucleotides. These elements were named short tandemly repeated repetitive (STRR) sequences. We used the three different Calothrix STRR sequences as probes to perform Southern hybridization experiments with DNAs extracted from various cyanobacterial strains, Bacillus subtilis, and Escherichia coli. The three different STRR sequences were found as repetitive genomic DNA components specific to the heterocystous strains tested. The role of the STRR sequences, as well as their possible use in taxonomic studies, is discussed.

Occurrence and distribution of gas vesicle genes among cyanobacteria.

Gas vesicles (GV) are specialized cell inclusions providing many aquatic procaryotes with buoyancy. In the cyanobacterium Calothrix sp. strain PCC 7601, at least four genes are involved in GV formation. One of those, gvpA1, encodes the major structural GV protein (70 amino acids) and belongs to a multigene family (gvpA1, gvpA2, gvpD). The fourth gene, gvpC, encodes a 162-amino-acid protein, the function of which is still unclear. We used the Calothrix gvpA1 and gvpC genes as probes to perform Southern hybridization experiments with DNA extracted from various cyanobacterial strains. The gvpA gene was found in all the strains that synthesize GV, indicating that its product is an obligatory component of GV. Furthermore, it was found to occur as multiple copies in most of the strains tested. The gvpC gene was only detected in some strains able to synthesize a large amount of GV within a short period. This suggests that the gvpC gene product is a dispensable protein for GV formation and is involved in the efficiency of the assembly process. Based on the occurrence of the gvp genes and on DNA-DNA hybridization patterns, genus assignments are discussed.

[Comparative study of 2 assay methods for serum isoniazid in 413 patients: microbiological method and high performance liquid chromatography]. / Etude comparative de 2 méthodes de dosage de l'isoniazide sérique chez 413 patients: méthode microbiologique, chromatographie liquide à haute performance.

Serum INH was assayed by 2 techniques over 4 years in 413 patients following the administration of a single test dose of 300 mg of isoniazid. The microbiological method measures the inhibitory activity of the serum on the growth of mycobacteria. The pharmacological method consists of high performance liquid chromatography with ultra-violet detection (HPLC). The mean difference in the assays performed by the 2 methods in each subject was 0.061 mcg/ml and the global correlation between the 2 assays was 0.76. Liquid chromatography also allows the simultaneous assay of acetyl INH. Thirty-three per cent of the subjects who received a test dose of 300 mg of INH had a serum INH concentration of between 1 and 2 mcg/ml at the third hour. This study therefore confirms the usefulness of a pre-treatment assay of INH and the good correlation of the results obtained with the 2 methods.

A new approach for molecular cloning in cyanobacteria: cloning of an Anacystis nidulans met gene using a Tn901-induced mutant.

A new strategy for molecular cloning in the cyanobacterium Anacystis nidulans R-2 is described. This strategy involved the use of a transposon and was developed for the cloning of a gene encoding methionine biosynthesis. A met::Tn901 mutant was isolated. Chromosomal DNA fragments were cloned in the Escherichia coli plasmid vector pACYC184. A recombinant plasmid carrying the inactivated met::Tn901 gene was selected after transformation to E. coli. The cloned met::Tn901 DNA fragment was used as a probe to select the corresponding A. nidulans R-2 wild-type met gene from a gene library prepared in E. coli, using the newly constructed shuttle cosmid vector pPUC29. When transformed into A. nidulans Met- mutants, this cloned gene allowed the mutants to grow prototrophically.

Wavelength modulation of phycoerythrin synthesis in Synechocystis sp. 6701.

The spectral dependence of phycoerythrin synthesis has been studied in a unicellular photautotrophic cyanobacterium, Synechocystis sp. 6701, in which phycoerythrin synthesis alone is under chromatic control. Cells were partially depleted of their phycobiliprotein pigments through nitrate starvation in the light. Addition of nitrate to the culture medium allowed synthesis of phycobiliproteins in the dark. This synthesis occurred at the expense of the glycogen reserve accumulated during the period of nitrate starvation. Monochromatic irradiations of short duration at lambda less than 590 nm induced increased phycoerythrin synthesis during dark incubation. Monochromatic irradiations of short duration at lambda greater than 590 nm prevented this synthesis. These effects were photoreversible. The spectral distribution showed a maximum at 540 nm for the potentiation of phycoerythrin synthesis, and one at 640 nm for its photoreversal.