Sensitivity to stress in the bivalve Macoma balthica from the most northern (Arctic) to the most southern (French) populations: low sensitivity in Arctic populations because of genetic adaptations?

The stress sensitivity, determined in copper exposureexperiments and in survival in air tests, and thegenetic structure, measured by means of isoenzymeelectrophoresis, were assessed in populations of theBaltic clam Macoma balthica (L.) from itssouthern to its northern distribution limit, in orderto test the hypotheses that near the distributionlimit the clams would be more stress sensitive andwould have a lower genetic variability. Thepopulations in west and north Europe show a stronggenetic resemblance. The populations in the sub-ArcticWhite Sea are genetically slightly different, and showa low stress sensitivity. The populations in theArctic Pechora Sea are genetically very distant fromthe other populations, and show the lowest stresssensitivity. Near the southern distribution limit, inagreement with the hypotheses, genetic variability islow and stress sensitivity high. On the other hand, incontrast to expectation, near the northerndistribution limit, in the populations of the PechoraSea, the genetic variability was higher, thus notreduced, and the stress sensitivity was low comparedto all other populations. Yet, it remains a questionif such is due to gradual physiologicalacclimatization (and ongoing differential selection)or to genetic adaptation.     

Variable thermal sensitivity as output of a circadian clock controlling the bimodal rhythm of temperature choice in the ant Camponotus mus

Along a thermal gradient and under a LD 1212 h cycle, nurse workers of the ant Camponotus mus select for the brood two different temperatures daily: 30.8°C at the middle of the light period (circadian phase = 90°), and 27.5°C 8 h later, during the dark period (CP = 210°). Brood-carrying activity proved to be self-sustained, running its two daily bursts free with a similar period of 23.5 h, under both LL and DD. The LD alternation acted as a strong Zeitgeber. A phase-delay of the LD 1212 h cycle reset the overt rhythm at once, being both daily events locked-on to the delayed light: dark transition. However, changes in expression, non-occurrence, or even splitting of the two daily brood-carrying events during resetting depended on the phase of the delayed DL transition. By comparing the occurrence of activity with predictions based on a threshold curve of thermal sensitivity, results indicated that an immediate resetting of the involved pacemaker actually takes place. Nurse workers do not directly control the total time spent by the brood at the selected temperature. Instead, the endogenously-driven thermal sensitivity triggers their thermal-searching behavior at two critical times of the day, when environmental temperature is expected to reach its maximum and minimum.     

RAD51 homologues in Xenopus laevis: two distinct genes are highly expressed in ovary and testis

The RAD51 gene is a eukaryotic counterpart of the Escherichia coli recA gene which is involved in genetic recombination. Two distinct Xenopus laevis RAD51 cDNA clones (XRAD51.1 and XRAD51.2) were isolated from an oocyte cDNA library using the human RAD51 cDNA (HsRAD51) as a probe. Sequence analysis revealed that 98.2% of the amino-acid residues were identical between XRAD51.1 and XRAD51.2, and that both were 95% identical to HsRAD51. Both of the XRAD51 genes were expressed at a higher level in ovary and testis than in other somatic tissues, suggesting their involvement in meiotic recombination. The expression of XRAD51.1 was about eightfold in excess of that of XRAD51.2 in all of the tissues examined. Analysis of the rates of synonymous substitution in the coding sequences of the two XRAD51 suggests that these two genes diverged about 50 million years ago. The structural similarities of the XRAD51 proteins to RecA in E. coli and Rad51 in yeasts or vertebrates are discussed.     

Properties of phosphoenolpyruvate carboxylase in desalted extracts from isolated guard-cell protoplasts

Properties of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) obtained from isolated guard-cell protoplasts of Vicia faba L. were determined following rapidly desalting of the extract on a Sephadex G 25 column. The activity of PEP carboxylase was measured as a function of PEP and malate concentration, pH and K⁺ concentration within 2–3 min after homogenization of the guard-cell protoplasts. The activity of this enzyme was stimulated by PEP concentrations of 0.1 to 0.75 mM and by K⁺ ions (12 mM), but inhibited by PEP concentrations above 1 mM and by malate. Changes in the K_m(PEP) and V_max values with increasing malate concentrations (2.5 and 5 mM) indicate that the malate level, varying in relation to the physiological state of guard cells, plays an important role in regulating the properties of phosphoenolpyruvate carboxylase.Abbreviations CAM Crassulacean acid metabolism - GCP guard-cell protoplast - PEP phosphoenolpyruvate Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday     

The sensitivity of halobacteria to antibiotics

Abstract Eleven species of the genera Halobacterium, Halococcus and the recently proposed Haloarcula were tested by the macro-broth dilution method for their sensitivity to 20 antibiotics with different modes of action. The most active were bacitracin, erythromycin, haloquinone, rifampicin and novobiocin. Resistant mutants of H. mediterranei to bacitracin, chloramphenicol and josamycin were obtained with frequencies of spontaneous mutation between 10⁻⁴ and 10⁻⁷.     

Transformation of Kluyveromyces lactis with the kanamycin (G418) resistance gene of Tn903

Direct selection of Kluyveromyces lactis resistant to the antibiotic G418 following transformation with the kanamycin resistance gene of Tn903 required the development of a procedure for producing high yields of viable spheroplasts and for the isolation of autonomous replication sequences (ARS). To obtain high yields of viable spheroplasts, cells were treated with (1) a thiol-reducing agent (L-cysteine), and (2) a high concentration of an osmotic stabilizer, 1.5 M sorbitol. Several ARS-containing plasmids were selected from a K. lactis recombinant DNA library in K. lactis and in Saccharomyces cerevisiae. Two of four ARS clones selected in K. lactis promoted transformation frequencies of 5-10 X 10(2) G418-resistant cells/micrograms of plasmid DNA. This frequency of transformation was at least twice as high as with ARS clones selected in S. cerevisiae. The stability of ARS-containing plasmids varied; after 20 generations of growth in the presence of G418, 16-38% of the cells remained resistant to the drug. In the absence of selection pressure less than 5% of the cells retained the drug-resistance phenotype. Plasmids containing the ARS1 or 2 mu replicon of S. cerevisiae failed to transform K. lactis for G418 resistance. Inclusion of S. cerevisiae centromere, CEN4, in a K. lactis ARS recombinant plasmid did not increase the stability of the plasmid in K. lactis, and marker genes on the vector segregated predominantly 4-:0+ through meiosis. We conclude that neither the ARS sequences or the centromere of S. cerevisiae was functioning in K. lactis.     

Structural properties of the zinc site in Cu,Zn-superoxide dismutase; Perturbed angular correlation of gamma ray spectroscopy on the Cu, 111Cd-superoxide dismutase derivative

The Zn(II) site of the dimeric Cu(II),Zn(II)-superoxide dismutase from Saccharomyces cerevisiae has been examined by means of perturbed angular correlation of gamma rays (PAC) on the Cu(II),Cd(II)- and Cu(I),Cd(II)-superoxide dismutase. The PAC spectrum for the Cu(II),Cd(II) enzyme reveals two different, pH independent, coordination geometries for the Cd site. Removal of Cu(II) does not affect the PAC spectrum, which suggests that Cu(II) and Cd(II) do not share a common histidine side chain as ligand. The results are consistent with either an equilibrium between two coordination geometries for Cd(II) in each subunit or a difference in the structure of the Cd(II) site in the two subunits. In contrast, in the reduced enzyme only one structure is present, identical for the two subunits.     

Nitrous acid mutagenesis of duplex DNA as a three-component system.

Purified native Hemophilus influenzae DNA is relatively insusceptible to nitrous acid (NA) mutagenesis in vitro, but is readily mutated following denaturation. NA mutagenicity for duplex DNA is significantly increased in the presence of various alcohols, glycols, phenols or primary amines. Phenol-extracted DNA contains dissociable contaminants of low molecular weight that enhance NA mutagenesis. Enhancement of NA mutagenesis by phenol and by spermine is due to the formation of unstable molecular species. We propose that reactive organic nitroso compounds are formed which then serve as delivery vehicles to promote mutagenicity of native DNA, perhaps via transnitrosation reactions. Similar reactions probably occur in vivo to promote NA-induced base substitution (but not frameshift) mutations in Salmonella typhimurium and in Escherichia coli. The possible significance of these observations to carcinogenesis is discussed.     

Mitochondrial mutagenesis in Saccharomyces cerevisiae. III. Nitrous acid.

Nitrous acid (NA) induced mutations efficiently in mitDNA, conferring resistance to erythromycin and weakly induces mit- mutations. In some strains of yeast it also enhanced rho- mutations. The frequencies of nuclear and mitochondrial mutations induced with NA are compared.     

Survival and transfer in the human gut of poorly mobilizable (pBR322) and of transferable plasmids from the same carrier E. coli

We examined the survival of a host Escherichia coli K-12 bacterium containing two transferable plasmids (pLM2, pSL222-4) and one poorly mobilizable plasmid (pBR322), and the transfer of these three plasmids to endogenous bacteria in the human intestinal tract. The survival of this plasmid-carrying host organism in four human volunteers was 3.5 to 6 days at recovery rates of 10^?1 to 10^?4. This finding was similar to our previous survival data on the same organism bearing a single plasmid. The K-12 strain appeared to be under a strong selective disadvantage in the human gut, since, even when bearing a tetracycline-resistant plasmid, its titer did not increase despite the administration of tetracycline. Studies of transferability showed that, while the transfer-depressed incFII plasmid pSL222-4 transferred at a frequency of 10^?1 in culture, its transfer in the human gut was much less frequent. The number of new recipients per donor cell ingested was about 10^?5, which included new recipients arising by multiplication. The recovery of pSL222-4 transcipients was enhanced by the administration of tetracycline on day 6. Neither the transfer-repressed, broad host range incP plasmid pLM2, nor the plasmid pBR322, could be detected in any endogenous host bacteria. Using the transfer and mobilization frequencies obtained in culture and the number of new recipients of pSL222-4 in the intestinal tract, we estimated that any in vivo mobilization of pBR322 to a new recipient could not occur at a frequency higher than 10^?12.