Paleoceanographic interpretations of coccoliths and oxygen-isotopes from the sediment surface of the southwest Indian Ocean

The distribution of forty-four coccolithophore species in one hundred deep-sea core-tops from the southwest Indian Ocean is described. Three coccolith assemblages have been recognised (Maputo, Agulhas Current and deep water) by the relative abundances of four ecologically significant coccolithophore species (Gephyrocapsa oceanica, Emiliania huxleyi, Calcidiscus leptoporus and Umbilicosphaera sibogae). Their biogeographical distribution appears to be related to water temperature, nutrient concentration and dissolution.The degree of preservation of coccoliths and foraminifera indicates that the carbonate lysocline lies somewhere between 3500 and 4000 m, resulting in the concentration of dissolution-resistant microfossils below this depth.Stable oxygen isotope ratios of the planktonic foraminiferal species Globigerinoides sacculifer range between −1.5 to −1.0‰ PDB (equal to 22.8–25.1°C) and occur in a narrow band on the sea floor beneath the “A” route of the Agulhas Current.These values are about 0.5 per mil PDB lighter than samples analyzed on either side of this band and can be explained by the Agulhas Current's elevated temperature at the ocean surface of 2–3°C. Thus an oxygen isotope imprint of the Agulhas Current exists beneath it on the sea floor.The Agulhas Current is probably the major factor influencing sedimentation, sediment-distribution patterns and geological features in the study area. At present it is voluminous and fast flowing, possibly eroding sediments up to 2500 m below the surface.The oxygen-isotope ratios and nannoplankton counts obtained in this study indicate, however, that the majority of samples are most probably recent or at least not older than 85,000 years. This implies that sediments are accumulating on the ocean floor and that the Agulhas Current does not have a pronounced erosional influence, at least in areas from which cores were retrieved for this study.     

Effect of Phosphate on the Corrosion of Carbon Steel and on the Composition of Corrosion Products in Two-Stage Continuous Cultures of Desulfovibrio desulfuricans

A field isolate of Desulfovibrio desulfuricans was grown in defined medium in a two-stage continuous culture apparatus with different concentrations of phosphate in the feed medium. The first state (V1) was operated as a conventional chemostat (D = 0.045 h⁻¹) that was limited in energy source (lactate) or phosphate. The second stage (V2) received effluent from V1 but no additional nutrients, and contained a healthy population of transiently starved or resting cells. An increase in the concentration of phosphate in the medium fed to V1 resulted in increased corrosion rates of carbon steel in both V1 and V2. Despite the more rapid corrosion observed in growing cultures relative to that in resting cultures, corrosion products that were isolated under strictly anaerobic conditions from the two culture modes had similar bulk compositions which varied with the phosphate content of the medium. Crystalline mackinawite (Fe₉S₈), vivianite [Fe₃(PO₄)₂ · 8H₂O], and goethite [FeO(OH)] were detected in amounts which varied with the culture conditions. Chemical analyses indicated that the S in the corrosion product was almost exclusively in the form of sulfides, while the P was present both as phosphate and as unidentified components, possibly reduced P species. Some differential localization of S and P was observed in intact corrosion products. Cells from lactate-limited, but not from phosphate-limited, cultures contained intracellular granules that were enriched in P and Fe. The results are discussed in terms of several proposed mechanisms of microbiologically influenced corrosion.     

Hormone-dependent processing of the avian progesterone receptor

Avian progesterone receptor exists as two forms, A and B, with molecular weights of 79,000 and 110,000 daltons, respectively. The origin and significance of these two forms is an area of active investigation and debate. Monoclonal antibodies produced against these two forms were used to examine receptor stability in cytosol and changes in the receptor forms induced by hormone binding. The lability of hormone binding at elevated temperatures is well documented. Analysis by Western blotting showed the receptor was stable in freshly prepared oviduct cytosol for 2 hr at 37°C, while hormone binding was lost within 30 min. However, loss of receptor through degradation was seen when cytosol was prepared from frozen tissue or when homogenization was excessive. Progesterone was injected into diethylstilbestrol-stimulated chicks to examine, in vivo, effects of hormone treatment on receptor forms in the cytosol and nuclear fractions. Progesterone treatment caused a time- and dose-dependent conversion of the A receptor to a form (A′) with a slower electrophoretic mobility. The cytosolic progesterone receptor was divided equally between the B and A forms, while the nuclear receptor was predominantly A′. The amount of nuclear receptor was consistently less than cytosolic receptor. Receptor phosphorylation was analyzed by incubating tissue minces with [³²P]orthophosphate with or without progesterone followed by immune isolation of receptor forms. Progesterone treatment caused a time-dependent increase in cytosol receptor phosphorylation which was evident after 5 min of treatment. This phosphorylation was observed with both the A and B receptor forms. The results indicate that receptor phosphorylation is a very early event during progesterone action.     

Defective production of anti-herpes simplex virus antibody by neonatal mice. Reconstitution with Ia+ macrophages and T helper lymphocytes from nonimmune adult syngeneic mice

Both neonatal humans and mice are exquisitely susceptible to severe HSV infection. We have now documented a profound defect in the ability of neonatal C57BL/6 mice to produce anti-HSV ADCC antibody. This ability is acquired over the first 2 to 4 wk of life. Reconstitution of neonatal mice by i.p. injection of peritoneal cells from adult nonimmune syngeneic mice both affords dose-dependent protection against lethal HSV infection and reconstitutes the antibody-production defect. By cell-separation techniques (adherence, nylon wool column purification, B cell panning) and cell ablation techniques (silica treatment, irradiation, anti-T cell, anti-Ia, anti-Lyt-1.2 and anti-Lyt-2.2 monoclonal antibodies plus complement treatment) the subpopulations involved in the antibody production reconstitution of neonatal mice by adult cells were identified. These include both an Ia+, radioresistant, adherent, silica-sensitive macrophage population and a nylon wool column-purified, radiosensitive, anti-T, anti-Lyt-1.2-sensitive helper T cell population. The latter cell may be substituted for by concanavalin A-stimulated lymphokine-containing spleen cell supernatants or human recombinant IL 2. In addition to reconstitution of ADCC antibody production, the same cell populations, or cells plus lymphokine-containing supernatants or IL 2, protected the newborn mice from lethal HSV infection. Further characterization of this system and of soluble replacement factors has implications for therapy or immunoprophylaxis of human neonates with, or at risk of, HSV infection.     

Analysis of fidelity mechanisms with eukaryotic DNA replication and repair proteins

We are investigating the mechanisms for producing or avoiding errors during DNA synthesis catalyzed by DNA replication and repair proteins purified from eukaryotic sources. Using assays that monitor the fidelity of a single round of DNA synthesis in vitro, we have defined the error frequency and mutational specificity of the four classes of animal cell DNA polymerases (alpha, beta, delta, gamma), and the fidelity of an SV40 origin-dependent DNA replication complex in extracts of HeLa cells.     

Rock-Climbing Injuries in Yosemite National Park

This study was presented in part at the annual meeting of the Wilderness Medical Society at Aspen, Colorado, in August 1986 and at “Mountain Medicine 1987,” Leavenworth, Washington, in November 1987.We questioned 220 injured rock climbers or their partners seen consecutively at the Yosemite (California) Medical Clinic over 3 ½ years regarding details of their accidents. Injury type and location were extracted from medical records and severity quantified. The National Park Service rescued 27% of the climbers. Injured climbers were characteristically male (88%) and experienced (mean 5.9 years) and typically fell while leading climbs (66%). Among 451 injuries, 50% were to the skin or subcutaneous tissues, while 28% involved the lower extremity and were predominantly fractures. In terms of each climber''s most severe injury (n = 220), 45% involved the lower extremities (30% from the ankle alone). Head injury or hypothermia caused 12 of 13 fatalities, showing the lowest case-fatality rate reported to date among injured climbers (6%). Rescue personnel successfully managed airways in victims of head injuries, anticipated and treated complications of hypothermia, and stabilized fractures. Victims requiring immediate extensive surgical intervention or blood transfusion usually died before rescue could be effected.     

Protists have divergent effects on bacterial diversity along a productivity gradient

Productivity and predation are thought to be crucial drivers of bacterial diversity. We tested how the productivity–diversity of a natural bacterial community is modified by the presence of protist predators with different feeding preferences. In the absence of predators, there was a unimodal relationship between bacterial diversity and productivity. We found that three protist species (Bodo, Spumella and Cyclidium) had widely divergent effects on bacterial diversity across the productivity gradient. Bodo and Cyclidium had little effect on the shape of the productivity–diversity gradient, while Spumella flattened the relationship. We explain these results in terms of the feeding preferences of these predators.