Inhibition of growth of Escherichia coli by lactose and other galactosides

A study has been made of the inhibition of growth caused by the addition of lactose or other galactosides to lac constitutive Escherichia coli growing in glycerol minimal medium. The effect was greater at pH 5.9 and pH 7.9 than at pH 7.0. Inhibition of growth by lactose was observed also in the case of a β-galactosidase negative mutant. However, a lacY mutant, which has a defect in the entry of protons normally coupled with galactoside transport, showed only slight inhibition of growth on the addition of galactosides. In the case of the parental strain the addition of lactose resulted in a sharp fall in ΔpH across the cell membrane and a reduction in intracellular ATP, and the recovery was slow. Under the same conditions the lacY mutant showed a smaller and only transient effect. It is postulated that the sudden entry of protons associated with lactose uptake lowers the protonmotive force, reducing the ATP levels and inhibiting growth of the cells. This hypothesis would account also for the selection of lacY mutants found when E. coli is grown in the presence of isopropyl-β-d-thiogalactoside.     

CHARACTERIZATION OF MICROBIALITE-FORMING CYANOBACTERIA IN A TROPICAL LAGOON: TIKEHAU ATOLL, TUAMOTU, FRENCH POLYNESIA

Natural populations of benthic cyanobacteria in the lagoon of Tikehau Atoll in French Polynesia were studied using a polyphasic approach that combined field observations, LM, culturing, and molecular sequencing. The approach assessed their phenotypic (morphotypic and ecological) and genotypic diversity. Partial sequences (approximately 450 bp long) of the PCR-amplified 16S rRNA gene were obtained from both natural and cultured populations using cyanobacteria-specific primers. The sequences obtained clustered into six separate phylogenetic clusters in relation to the complete set of 16S rRNA sequences available in public databases. Phylogenetic clustering correlated in many cases with some morphological characteristics. For example, Spirulina subsalsa could be identified to the morphospecies level using both molecular and microscopic approaches. Morphotypes identified as Symploca hydnoides (Kütz. ex Gomont) TK22, Phormidium sp. TK1, and P. laysanense (Lemmerman) TK14 formed a distinct cluster. The morphogenus Hydrocoleum (Blennothrix) clustered interestingly close to the morphologically similar, but planktonic, marine cyanobacterium Trichodesmium , suggesting a relationship. Other sequences belonging to morphotaxa with very narrow trichomes were found to be polyphyletic. Enrichment cultures, with inoculum obtained from field populations, were followed over a period of 18 months. Dominance in all cultures shifted over time in favor of a set of cyanobacterial strains with narrow trichomes, which were phenotypically and phylogenetically different from natural populations dominating the original samples. Sequences from strains enriched by cultivation clustered into two well-defined phylogenetic groups, possibly identifying new taxa. These clusters may represent a niche of opportunistic species, evolved to exploit short-term nutrient spikes in the environment.     

Factors affecting egg dimensions and breeding success in the Cory''s Shearwater(Calonectris diomedea) of Selvagem Grande

Summary Eggs of the Cory's ShearwaterCalonectris diomedea borealis of Selvagem Grande (Madeira, 30°09N, 15°52W), show high variability in size and shape between females, while for each individual both are correlated over two seasons. During the first breeding years, females lay larger and more rounded eggs as their experience (number of years since first breeding) increases. Age (number of years since birth) probably has an effect on egg size but adult size has none. No important differences between the two years of study has been observed and no inter-colony variation is apparent. Finally, breeding success is directly linked to egg size but not to egg shape.

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Eigröße und Bruterfolg von Gelbschnabelsturmtauchern(Calonectris diomedea borealis) auf Selvagem Grande

Zusammenfassung Die Größe und Form der Eier des GelbschnabelsturmtauchersCalonectris diomedea borealis von Selvagem Grande (30°09N, 15°52W) variieren zwischen verschiedenen Weibchen erheblich, die einzelnen Weibchen legen jedoch in Folgejahren gleich große Eier. Erfahrenere Weibchen legen größere und rundere Eier. Ältere Weibchen legen größere Eier. Das Alter hat keinen Einfluß auf die Eigröße. Zwischen den beiden Untersuchungsjahren (1996 und 1997) gab es keine Unterschiede, auch nicht zwischen verschiedenen Kolonien. Bruterfolg und Eigröße waren positiv korreliert.

     

Nest structure and colony cycle of the Allegheny mound ant,Formica exsectoides Forel (Hymenoptera: Formicidae)

Summary The nest structure and colony cycle of a population of Allegheny mound ants,Formica exsectoides, were examined in central Michigan. The dispersion pattern of mounds was random. Nest structure and presence of brood were primarily determined by excavation of twenty-three nests over three intervals from June through September. Additional excavations of five nests in 1990 and ten nests in 1991 provided further details on nest structure and colony cycle. Most galleries occurred within the mound and upper 30 cm of soil, but some activity reached depths of 100 to 270 cm. Depth of nests showed little correlation with external measurements of height and diameter. Immature stages were recovered from two strata: the upper 20 cm of nest and mound and the lowest nest depths. Alate sexual forms were found in or near the mound in July, and numerous dealate queens were collected in September from peripheral galleries near the soil surface.     

In vitro modulation of canine polymorphonuclear leukocyte function by granulocyte-macrophage colony stimulating factor

Granulocyte-macrophage colony stimulating factor (GMCSF) promotes the growth of granulocytes and macrophages from undifferentiated bone marrow cells and modulates the oxidative responses of polymorphonuclear leukocytes (PMN) to endogenous chemoattractants. We found that,in vitro, naturally occurring glycolsylated human GMCSF does not disturb the resting canine PMN membrane potential, may attentuate PMN oxidative responses to PMA, and is, to a small degree, chemotaxigenic. GMCSF, however, inhibits PMN chemotaxis to zymosanactivated plasma (ZAP). Compared to temperature controls, GMCSF (1-100 U/ml) produced up to 1.5-fold increases in H₂O₂ production after 15 minutes, while phorbol myristate acetate (PMA) treated cells increased H₂O₂ production 8–12-fold after 15 minutes. Preincubation of cells with GMCSF (1–100 U/ml) prior to PMA stimulation significantly reduced the H₂O₂ levels induced by PMA. H202 production was inhibited up to 15% after 15 minutes of GMCSF preincubation and up to 40% after 60 minutes of preincubation. As a chemotaxigenic agent, GMCSF (10–1000 U/ml) was able to elicit 49%–102% increases in quantitative cellular migration, compared to random migration. Total cellular chemotaxis to GMCSF was < 30% of the response to ZAP. Preincubation of PMNs with GMCSF for 15 minutes significantly inhibited ZAP-induced cellular migration. Human GMCSF does not appear to activate canine PMNin vitro and may actually down-regulate PMN inflammatory responses.Supported by the Armed Forces Radiobiology Research Institute, Defense Nuclear Agency, under work unit No. 00082. Views presented in this paper are those of the authors; no endorsement by the Defense Nuclear Agency has been given or should be inferred. Research was conducted according to the principles enunciated in the Guide for the Care and Use of Laboratory Animals prepared by the Institute of Laboratory Animal Resources, National Research Council.     

Structural disorder in proteins

The refinement of X-ray structural data gives the mean square displacements, x ², at each position in the protein molecule. In order to get information on the significance of such values different refinement methods have been compared. The metmyoglobin structure was determined at 300 K and x ²-values were obtained with the restrained refinement procedure in reciprocal space of Konnert and Hendrickson. A comparison with the results of Frauenfelder et al. was used for an error estimation. The inclusion of surface bound water increases the accuracy of the results but does not change the general picture. For erythrocruorin (CTT3) a refinement was performed in reciprocal space and compared with a refinement in real space performed earlier. The x ²-values obtained from both procedures are similar although the reciprocal space refinement gives results which are physically more reasonable.A comparison of the disorder in myoglobin and erythrocruorin showed that the structural similarity results in a similarity in the disorder. Contacts of molecules in the crystal do not dominate the disorder although they locally influence x ²-values. CTT3 shows large disorder in the heme region in contrast to myoglobin. The differences in the rigidity of the F-helix can be correlated with the oxygen affinities supporting models for O₂ binding developed by Frauenfelder et al.     

Differentiation betweenPhaeocystis pouchetii (Har.) Lagerheim andPhaeocystis globosa Scherffel

An Arctic clone ofPhaeocystis pouchetii LAGERHEIM was compared toPhaeocystis globosa SCHERFFEL isolated from the southern North Sea with regard to temperature tolerance and colony shapes. Already youngP.pouchetii colonies (<100 m) show the typical distribution of the cells in groups, separated from each other by wide zones of cell-free mucilage; the maximum colony size is ca 2 mm in diameter.P.pouchetii colonies form clouds with bubble-like vesicles, spherical colony-shapes are seldom found.P.globosa colonies are spherical up to a size of 2 mm; the cells are distributed homogeneously over the periphery of the colonies. A pouchetii-like distribution of cells never occurs either in the spherical young colonies or in the pear-shaped old colonies (size up to 8 mm). A development from the colony shape of the globosa-type to the pouchetii-type or vice versa was never found. Therefore the colony shape has to be considered a constant distinctive character. Single cells ofP.pouchetii andP.globosa cannot be separated from each other by using the light microscope; this also holds for the flagellates and the non-motile cells.P.pouchetii grows well between 0°C and 14°C,P.globosa between 4°C and 22°C, respectively. Because of the distinctive differences in the morphology of the colonies and the differences in temperature tolerances we propose thatPhaeocystis globosa should no longer be considered conspecific withPhaeocystis pouchetii.