Goose-mediated nutrient enrichment and planktonic grazer control in Arctic freshwater ponds.

A dramatic increase in the breeding population of geese has occurred over the past few decades at Svalbard. This may strongly impact the fragile ecosystems of the Arctic tundra because many of the ultra-oligotrophic freshwater systems experience enrichment from goose feces. We surveyed 21 shallow tundra ponds along a gradient of nutrient enrichment based on exposure to geese. Concentrations of total phosphorus (P) and dissolved inorganic nitrogen (DIN) in the tundra ponds ranged from 2-76 to 2-23 microg l(-1) respectively, yet there was no significant increase in phytoplankton biomass (measured as chlorophyll a; range: 0.6-7.3 microg l(-1)) along the nutrient gradient. This lack of response may be the result of the trophic structure of these ecosystems, which consists of only a two-trophic level food chain with high biomasses of the efficient zooplankton grazer Daphnia in the absence of fish and scarcity of invertebrate predators. Our results indicate that this may cause a highly efficient grazing control of phytoplankton in all ponds, supported by the fact that large fractions of the nutrient pools were bound in zooplankton biomass. The median percentage of Daphnia-N and Daphnia-P content to particulate (sestonic) N and P was 338 and 3009%, respectively, which is extremely high compared to temperate lakes. Our data suggest that Daphnia in shallow arctic ponds is heavily subsidized by major inputs of energy from other food sources (bacteria, benthic biofilm), which may be crucial to the persistence of strong top-down control of pelagic algae by Daphnia.

Effects of inhaled hexamethylene diisocyanate (HDI) on guinea pig cholinesterases.

Hexamethylene diisocyanate, HDI, a starting material in the production of many polyurethane products, was found to inhibit stoichiometrically mammalian and electric eel cholinesterases in an in vivo system (W. E. Brown, A. H. Green, M. H. Karol, and Y. Alarie , 1982, Toxicol . Appl. Pharmacol. 62, 45-52). The current study examined in vivo effects on guinea pig cholinesterases resulting from inhalation of HDI. Guinea pigs were exposed to atmospheres of 0.5, 1.8, or 4.0 ppm HDI (ceiling value = 0.02 ppm) for up to 6 hr. Blood samples were drawn prior to exposure and at specified times during exposure. No inhibition of serum cholinesterase was detected following exposure to 0.5 ppm HDI for 6 hr, to 1.8 ppm HDI for 2 hr, or to 4.0 ppm HDI for 3 hr. Similarly, no inhibition was detected when erythrocytes from each blood sample were assayed for acetylcholinesterase activity. Last, animals were sacrificed and cholinesterase activity determined in bronchial lavage fluid. Enzyme levels of HDI-exposed animals were not significantly different (P greater than 0.05) from those of control animals exposed to water vapor. In conclusion, although in vitro experiments had demonstrated potent anticholinesterase activity by HDI, in vivo inhalation exposure of guinea pigs to HDI at concentrations 25-200 times above the recommended (ACGIH) ceiling value did not produce measurable inhibition of cholinesterase activity.

Morphology of cells and hemagglutinogens of Bordetella species: resolution of substructural units in fimbriae of Bordetella pertussis.

The morphology of cells and the hemagglutinogens isolated from cultures of Bordetella pertussis, Bordetella bronchiseptica, and Bordetella parapertussis were studied by electron microscopy with the negative-staining technique. Cells of all three species had long, thin (3 nm thick), peritrichously arranged fimbriae on the cell surface. Similar structures were found in purified hemagglutinogen preparations together with shorter fimbrial structures 3 nm thick and from 40 to 100 nm long. In one experiment, long, thin fimbriae isolated from B. pertussis were found to be arranged in a crystalline structure on the specimen grid after negative staining. Optical diffraction analysis with a filtering technique performed on micrographs of these structures revealed 12.5-nm-long substructures within individual fimbriae. Further analysis resolved each of these structures into three globules, a central globule 3.5 nm in diameter and two diametrically opposed globules 2.5 nm in diameter. Based on this substructural composition, it is suggested that subunits of the individual fimbriae are connected by fragile regions. The presence of such regions would explain the size heterogeneity of the filamentous structures observed in preparations of hemagglutinogens isolated from cultures of B. pertussis and B. bronchiseptica. The concept that the short filamentous structures present in purified preparations of hemagglutinogens originate from the surface fimbriae present on the cells is supported.

In vitro stimulation of human lymphocytes by Bordetella Pertussis.

Bordetella pertussis (B.p.) induces blast transformation of human lymphocytes; whole killed B.p. are more efficient than extracts obtained by sonication. Similar responses were obtained with each of the four strains used in the Danish pertussis vaccine. B.p. with low amounts of Protective Antigen and Histamine-Sensitizing Factor also induced lymphocyte transformation, but were less toxic to the lymphocytes at high concentrations. The supernatants of B.p. cultures were purified with respect to Lymphocytosis Promoting Factor; evidence is presented that these purified fractions possess T-lymphocyte mitogenic activity. Lymphocytes from all normal humans were stimulated by B.p., including cells from cord blood. Cells from childbearing women, obtained immediately after delivery, showed a general depression of lymphocyte transformation including the response to B.p. Children with whooping cough had a lower lymphocyte response to B.p. than healthy children. A highly significant correlation was observed between the responses to B.p. and to E. coli in the adults and newborn examined. It is concluded that the major part of the lymphocyte transformation induced by B.p. is non-specific.

Études sur la bacterie de la lèpre / Studies on the leprosy bacterium

La question de la contagiosit‚ de la lèpre n'a pas frait de progres dans ces dernières ann‚es, malgr‚ les travaux de Neisser (1) et Kubner (2).