Eucampia Index as an indicator of the Late Pleistocene oscillations of the winter sea-ice extent at the ODP Leg 119 Site 745B at the Kerguelen Plateau

A new paleoenvironmental proxy, Eucampia Index, was used to trace the Late Pleistocene oscillations of winter ice extent at ODP Leg 119, Site 745B (59° 35.71 S and 85° 51.60 E) on the Kerguelen Plateau. The index is calculated as the ratio of winter terminal to intercalary valves of the diatom Eucampia antarctica sensu lato. During the early Brunhes the winter sea-ice edge was positioned south from Site 745. It started expanding northward, closer to the site location soon after 0.4 Ma and progressed in a manner of a several wide oscillations. For approximately the last 0.1 Ma the winter sea-ice edge oscillated less and retained similar range of oscillations. The ice edge oscillated in periods which correspond closely to that of Milankovitch oscillations of Earth obliquity, although the significance of individual periods appears to vary in time.     

AlkB Dioxygenase Preferentially Repairs Protonated Substrates: SPECIFICITY AGAINST EXOCYCLIC ADDUCTS AND MOLECULAR MECHANISM OF ACTION*

Efficient repair by Escherichia coli AlkB dioxygenase of exocyclic DNA adducts 3,N⁴-ethenocytosine, 1,N⁶-ethenoadenine, 3,N⁴-α-hydroxyethanocytosine, and reported here for the first time 3,N⁴-α-hydroxypropanocytosine requires higher Fe(II) concentration than the reference 3-methylcytosine. The pH optimum for the repair follows the order of pK_a values for protonation of the adduct, suggesting that positively charged substrates favorably interact with the negatively charged carboxylic group of Asp-135 side chain in the enzyme active center. This interaction is supported by molecular modeling, indicating that 1,N⁶-ethenoadenine and 3,N⁴-ethenocytosine are bound to AlkB more favorably in their protonated cationic forms. An analysis of the pattern of intermolecular interactions that stabilize the location of the ligand points to a role of Asp-135 in recognition of the adduct in its protonated form. Moreover, ab initio calculations also underline the role of substrate protonation in lowering the free energy barrier of the transition state of epoxidation of the etheno adducts studied. The observed time courses of repair of mixtures of stereoisomers of 3,N⁴-α-hydroxyethanocytosine or 3,N⁴-α-hydroxypropanocytosine are unequivocally two-exponential curves, indicating that the respective isomers are repaired by AlkB with different efficiencies. Molecular modeling of these adducts bound by AlkB allowed evaluation of the participation of their possible conformational states in the enzymatic reaction.     

Effect of subinhibitory levels of selected antibiotics on susceptibility of Staphylococcus aureus strains to phagocytosis and killing by rabbit granulocytes

The aim of the study was to assess the of chosen antibiotics in subinhibitory concentrations (sub-MIC) on the sensitive of Staphylococcus aureus cells to phagocytosis and killing by rabbit granulocytes. The following antibiotics were used: cloxacillin, cefadroxil, cefuroxim, cefotaxim, gentamicin, netilmicin, lincomicin, doxycycline and riphamicin. A total of 144 S. aureus strains with varied sensitivity to these antibiotics were selected for the study. The experiment used granulocytes isolated from rabbit blood and S. aureus strains incubated for 18 h in TSB broth containing antibiotics in the concentrations of 0.1 MIC, 0.2 MIC and 0.5 MIC, and in the antibiotics-free medium. Phagocytosis was assessed by the method of differential staining with acridine orange and crystal violet, allowing simultaneous determination of phagocytised and killed S. aureus cell counts. The findings revealed that the culture of S. aureus in the presence of all the antibiotics used in subinhibitory concentrations increased significantly the susceptibility of most S. aureus strains to phagocytosis and killing by granulocytes. The above effect usually occurred in the concentrations of 0.1 MIC (54.2%), more seldom in 0.2 MIC (13%) and 0.5 MIC (15% of strains). Each group of S. aureus contained some which showed no change in susceptibility following culture with the chemotherapeutic agents in subinhibitory concentrations (26.3%). Insensitive strains to the subinhibitory effects were equally common among susceptible (27%), intermediate (23%) and resistant (26%) strains of S. aureus to the antibiotics used. No statistically significant reduction was noted in phagocytosis or killing by rabbit granulocytes. No correlation was observed between the susceptibility to the subinhibitory effects of the antibiotics involved and their biochemical mechanisms.     

Specific variability in Fe-enriched cultures from the equatorial Pacific

Water collected on the spring equatorial Pacific Joint GlobalOcean Flux Study (JGOFS) was placed in ultra-clean bottles inan incubator on deck under the direction of the team of J.H.Martin.Half of the bottles were enriched with 2.53 mM iron; the otherhalf served as controls. Cell counts increased, while the numberof species was reduced, in both the controls and the treatedsamples over the period of the experiment. Diatoms dominated,and after an early growth spurt in the Fe-enriched bottles,most diatom species showed greater growth in the controls atthe end of the 6 day experiment. However, as the experimentwas terminated, more cells overall were noted in the Fe-enrichedsamples, with the most abundant diatom, Cylindrotheca closterium.principally responsible for the difference. Growth rates werehigh in both the controls and the treated samples, with overallrates of 1.3–3.0 divisions day^–1 in the Fe-treatedsamples and 1.9–3.4 divisions day^–1 in the controls.The group of smaller pennate diatoms averaged 2.9 divisionsday^–1 in the Fe-treated samples and 3.3 divisions day^–1in the controls over the entire experiment.     

Relationship between propagule pressure and colonization pressure in invasion ecology: a test with ships' ballast

Increasing empirical evidence indicates the number of released individuals (i.e. propagule pressure) and number of released species (i.e. colonization pressure) are key determinants of the number of species that successfully invade new habitats. In view of these relationships, and the possibility that ships transport whole communities of organisms, we collected 333 ballast water and sediment samples to investigate the relationship between propagule and colonization pressure for a variety of diverse taxonomic groups (diatoms, dinoflagellates and invertebrates). We also reviewed the scientific literature to compare the number of species transported by ships to those reported in nature. Here, we show that even though ships transport nearly entire local communities, a strong relationship between propagule and colonization pressure exists only for dinoflagellates. Our study provides evidence that colonization pressure of invertebrates and diatoms may fluctuate widely irrespective of propagule pressure. We suggest that the lack of correspondence is explained by reduced uptake of invertebrates into the transport vector and the sensitivity of invertebrates and diatoms to selective pressures during transportation. Selection during transportation is initially evident through decreases in propagule pressure, followed by decreased colonization pressure in the most sensitive taxa.     

A new blue-pigmented hasleoid diatom,Haslea provincialis,from the Mediterranean Sea

Haslea provincialis Gastineau, Hansen & Mouget, sp. nov., is a new, morphologically semicryptic blue diatom discovered on the French shores of the Mediterranean Sea. Like H. ostrearia and H. karadagensis, H. provincialis shares the capacity to synthesize a marennine-like blue pigment. Sexual reproduction between clones of H. provincialis has been repeatedly observed and resulted in viable initial cells. There were no sexual interactions with sexually competent clones of H. ostrearia or H. karadagensis, as would be expected for a separate biological species. There are strong similarities between the H. provincialis pigment and the marennine produced by H. ostrearia, evidenced by UV-visible spectrophotometry and Raman spectrometry. However, unlike the marennine from H. ostrearia, no differences were found between the extracellular and the intracellular forms of the pigment in H. provincialis. This indicates that the synthesis pathways and excretion mechanisms among the three ‘blue’ Haslea may be species-specific. Molecular taxonomy and phylogeny (based on rbcL, cox1 and SSU V4 DNA sequences) confirmed the distinct position of this species among the blue Haslea species. Haslea provincialis occurs in environments from which H. ostrearia has already been reported (mostly based on the presence of the blue cell vacuoles). Possible species misidentifications and the impact of the complex geological history of the Mediterranean Sea on blue diatom diversification are also discussed.     

Pseudo-nitzschia species population dynamics in the Quoddy Region, Bay of Fundy

The population dynamics of Pseudo-nitzschia species from the Quoddy Region of the Bay of Fundy was examined in a field-based study. Five stations were sampled over a period of 11 weeks during the course of one discrete bloom episode in 2003 with seven species of Pseudo-nitzschia found and enumerated: P. americana, P. delicatissima, P. pseudodelicatissima, P. fraudulenta, P. pungens, P. seriata and P. subpacifica. We related species abundance to physical and chemical properties of seawater (transparency, fluorescence, silicate, phosphate, nitrite + nitrate, ammonia, nitrite, oxygen, sigma-t, tidal level, tidal state and total depth of water column) using canonical correspondence analysis (CCA) to identify factors explaining the greatest amount of variance in their temporal and spatial distribution patterns. Our results indicate that abundance of species and groups of species correlated well with certain specific chemical and physical properties of seawater. P. pseudodelicatissima and P. delicatissima abundance was positively correlated with nitrates and P. americana with depth of the water column. P. pungens was more abundant in samples with higher concentrations of phosphates and lower concentrations of nitrates. P. seriata abundance was negatively associated with total fluorescence. P. subpacifica and P. fraudulenta abundances were not statistically related to any of the variables examined. Our data therefore provides direction for testable, hypothesis driven experiments that could provide predictive insights into the occurrence of certain harmful algal bloom (HAB) species should specific environmental variables be further affected along the gradients extracted in this study.