Biomedical subjects

C Astier

Publications and source records attributed to C Astier.

40 records · Page 3Linked to original sources

PubMed1984

Photosynthetic mutants of the cyanobacteria Synechocystis sp. strains PCC 6714 and PCC 6803: sodium p-hydroxymercuribenzoate as a selective agent.

Among a wide range of potential selective agents examined, sodium p-hydroxymercuribenzoate successfully enriched for mutants of Synechocystis sp. strains PCC 6714 and 6803 defective in photosynthesis. When both photosystems I and II were operating, viability of wild-type cells decreased to between 5 X 10(-5) and 1 X 10(-6) after 5 h of incubation with 500 microM p-hydroxymercuribenzoate (strain 6714), and after 8 h with 200 microM (strain 6803). Between 0.1 and 0.5% of the survivors were stable mutants defective in different steps of photosynthesis. The compound was not mutagenic. It was less toxic to cells grown chemoheterotrophically in the dark or photoheterotrophically in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. p-Hydroxymercuribenzoate therefore killed only cells which were performing photosynthesis at high rates, thereby specifically selecting for mutants deficient in this process.

Chlorophyll↗

PubMed1983

Transformation in the cyanobacterium Synechococcus R2: improvement of efficiency; role of the pUH24 plasmid.

Systematic studies of the parameters influencing transformation efficiencies in Synechococcus R2 and its spontaneous pUH24 plasmid-minus variant S60, have led to substantial increases in these frequencies (up to 70 times for R2 and 9 times for S60) compared to those obtained by using previously published procedures. Important factors are the physiological state of the host cells (competence occurs at the transition from first to second exponential phases of growth) and the conditions of expression of the transferred characters (they must be exposed to progressively increasing concentrations of the selective agent). Consistently lower (about 30 times) efficiencies were obtained with the S60 strain, the only difference from the wild-type R2 that could be detected. Physiological functions of the pUH24 plasmid are discussed. The interest of the S60 strain as a host in gene cloning work is discussed in the light of published work suggesting inter-vector recombination in R2.

Cyanobacteria↗

PubMed1981

Contributions of Respiratory and Photosynthetic Pathways during Growth of a Facultative Photoautotrophic Cyanobacterium, Aphanocapsa 6714.

Comparison of the growth parameters and photosynthetic capacities of cells of Aphanocapsa 6714 under various growth conditions led to the following conclusions: (a), no enzymic regulation of CO(2)/glucose assimilation takes place in this strain; (b), functioning of photodependent phosphorylating pathways turns off oxidative ATP synthesis; (c), no efficient regulation of pigment synthesis exists in these cells; (d), most modulations of photosynthetic activities probably occur through structural modifications of the photosynthetic membranes (a small proportion of the pigments might appear as a nonintegrated pool in the cell and be sensitive to synthesis regulation); and (e), photosystem II activity would be dependent on light intensity in a discontinuous way, the consequence of this property being the appearance of two successive exponential phases during phototrophic growth in adequate light conditions.

Journal Article↗

PubMed1976

[A genetic transfer system in a cyanophyte of the genus Aphanocapsa].

The possibility of a genetic transfer, through a process of transformation, has been shown in a unicellular, facultative chemoheterotroph blue-green Algae, Aphanocapsa 6714. Similarly to the process described with Anacystis nidulans, the recipient strain becomes competent when the growth reaches its second, slower, exponential phase. The genetic marker conferring resistance to p-F-phenylalanine has been transferred with a frequency 20 to 100 times higher than that of the spontaneous mutations. The efficiency of transformation decreases by a factor of 70% when the transforming extract, which contains both DNA and RNA, is pretreated with DNase. This transfer process is compared to that observed with A. nidulans by several authors.

Cyanobacteria↗