Distribution of spring phytoplankton (mainly diatoms) in the upper 50 m of the Southwestern Atlantic Ocean (30-61{degrees}S)

This is the first study on diatom spatial patterns in relationto major oceanographic features along a megascale transect inthe Southwestern Atlantic Ocean and provides a comparison withdiatom distribution in surface sediments. Absolute abundancesof diatoms, silicoflagellates and dinoflagellates (>10-µmfraction) were assessed in 80 bottle samples from 5 to 50 m,retrieved in November 1993 at 20 stations (30–61°S)along 53°W. Siliceous phytoplankton were scarce in the northernhalf of the transect and in the south of 57°S (100–150cells L^–1), with a strong peak in the vicinity of thePolar Front (200 000 cells L^–1), whereas dinoflagellateswere more abundant at the northern stations (up to 24 000 cellsL^–1). In the south of 50°S phytoplanktonic cell densitieswere loosely (but significantly, r = 0.54, P < 0.01) associatedwith chlorophyll a, whereas in the north of this latitude, thisrelationship disappeared (r = 0.018, P > 0.1). In total,191 diatoms and 4 silicoflagellates were recorded. Changes indiatom assemblage compositions along the transect allowed identificationof five discrete areas: Subtropical (29°S), Northern Transitional(34–41°S), Southern Transitional (43–48°S),Subantarctic (49–54°S) and Antarctic (55–59°S),each characterized by a set of typical species. Diversity changedlittle with latitude, but numbers of species were higher inthe north of 40°S. Comparison of diatom assemblage makeupin the plankton and in the surface sediments shows very strongdisagreements, whereby cold water species are very significantlyover-represented in the sedimentary record, suggesting enhancedpreservation and strong subsurface equatorward advection ofthe cold water taxa.     

Resistance Determinants of a Highly Arsenic-Resistant Strain of Leptospirillum ferriphilum Isolated from a Commercial Biooxidation Tank

Two sets of arsenic resistance genes were isolated from the highly arsenic-resistant Leptospirillum ferriphilum Fairview strain. One set is located on a transposon, TnLfArs, and is related to the previously identified TnAtcArs from Acidithiobacillus caldus isolated from the same arsenopyrite biooxidation tank as L. ferriphilum. TnLfArs conferred resistance to arsenite and arsenate and was transpositionally active in Escherichia coli. TnLfArs and TnAtcArs were sufficiently different for them not to have been transferred from one type of bacterium to the other in the biooxidation tank. The second set of arsenic resistance genes conferred very low levels of resistance in E. coli and appeared to be poorly expressed in both L. ferriphilum and E. coli.     

Dynamic evolution of selenocysteine utilization in bacteria: a balance between selenoprotein loss and evolution of selenocysteine from redox active cysteine residues

Background  

Selenocysteine (Sec) is co-translationally inserted into protein in response to UGA codons. It occurs in oxidoreductase active sites and often is catalytically superior to cysteine (Cys). However, Sec is used very selectively in proteins and organisms. The wide distribution of Sec and its restricted use have not been explained.     

Combined effect of temperature and salinity on the Thermotolerance and osmotic pressure of juvenile white shrimp litopenaeus vannamei (Boone)

Thermotolerance (CTMax) was determined in L. vannamei in three salinities and five acclimation temperatures 20, 23, 26, 29 and 32 °C. In white shrimp, the CTMax was not significantly affected by salinity (P>0.05). A direct relationship was obtained between CTMax and acclimation temperature. The end point of the CTMax in L. vannamei exposed to different combinations of temperature and salinity was defined as the loss of the righting response (LRR). The acclimation response ratio (ARR) for the juveniles of white shrimp ranged from 0.42 to 0.49; values in agreement with other crustaceans from tropical and sub tropical climates. The osmotic pressure of the hemolymph was measured in control organisms and in organisms exposed to CTMax; significant differences were found in organisms maintained in 10 and 40 psu, but there were no significant differences in hemolymph osmotic pressure in those that were acclimated to 26 psu.     

Population-based modeling of the progression of apoptosis in mammalian cell culture

The production of biopharmaceuticals from mammalian cell culture is hindered by apoptosis, which is the primary cause of cell death in these cultures. As a tool for optimization of culture yield, this study presents a population-based model describing the progression of apoptosis in a monoclonal antibody (mAb)-producing Chinese hamster ovary (CHO) cell culture. Because mAb production does not cease when apoptosis begins, the model was designed to incorporate subpopulations at various stages in the progression of apoptosis. The model was validated against intracellular measurements of caspase activity as well as cell density, nutrient levels, and toxic metabolites. Since the specific details of apoptotic mechanisms have not been elucidated in this cell line, we employed a model comparison analysis that suggests the most plausible pathways of activation.     

Light‐based Regeneration Niches: Evidence from 21 Dipterocarp Species using Size‐specific RGRs

A continuing challenge in tropical ecology is to explain the coexistence of large numbers of rain forest tree species. One possible coexistence mechanism is partitioning of the highly variable and dynamic forest light environment, in which species that grow better in one light treatment grow worse in another. To test whether species respond differently to the light environment, we estimated growth rates of 21 Dipterocarpaceae species from Malaysian Borneo grown in shade houses for 2 yr in three light treatments (0.3%, 3%, and 18% full sunlight). We made regular measurements of height, diameter, and aboveground biomass, enabling us to calculate growth rates for each response. We estimated size‐specific growth rates using nonlinear mixed‐effects models, as average relative growth rate was strongly size dependent. For all species, the greatest diameter growth rate was achieved in 18 percent full sunlight, whereas for five of the twenty‐one species, the greatest height growth rate was achieved in three percent full sunlight. We investigated correlations among growth rates in different light treatments, but no negative correlations were found, indicating that species growing well in one light treatment did not grow poorly in the others. There were substantial crossovers, however, in species ranks among the three light treatments, indicating that there was no single growth rate hierarchy common to all light treatments. The lack of a single consistent growth hierarchy across light treatments indicates that heterogeneity in the forest light environment could contribute to the maintenance of the diversity of Dipterocarpaceae found in lowland Bornean rain forests via light‐based regeneration niches.     

Echinococcus granulosus: different cytokine profiles are induced by single versus multiple experimental infections in dogs

Modulation of host responses is an important strategy by which parasites ensure successful establishment and persistence. Host counteraction against this modulation may be required for the host to develop resistance to infection. In this pilot study, experimental infection of dogs with Echinococcus granulosus induced a strong polarization of the cytokine response towards a Th2 phenotype. Consecutive rounds of infection and cure induced resistance to infection resulting in a dramatically lower parasite burden. Repeatedly-infected resistant dogs also lost immune polarization and developed a balanced Th1/Th2 response. No major differences were observed in the production of regulatory cytokines (IL-10, TGF-β) between dogs with high parasite load and dogs with only few intestinal parasites. These results suggest that E. granulosus-driven immunomodulation contributes to successful infection in the definitive host. This information might be relevant for the development of more effective vaccines against this stage of the parasite.     

Contrasting effects of selenite and tellurite on lipoamide dehydrogenase activity suggest a different biological behaviour of the two chalcogens

The effects of selenite and tellurite on the mammalian enzyme lipoamide dehydrogenase were compared. Selenite acts as a substrate of lipoamide dehydrogenase in a process requiring the presence of lipoamide. In contrast, tellurite is a potent inhibitor, effective in the low micromolar range. The inhibitory effect of tellurite on lipoamide dehydrogenase is partially reverted by dithiothreitol indicating the participation of the thiol groups of the enzyme. Tellurite, but not selenite, stimulates the diaphorase activity of lipoamide dehydrogenase. In a mitochondrial matrix protein preparation, which contains lipoamide dehydrogenase, an inhibitory action similar to that observed on the purified enzyme was also elicited by tellurite. Human embryonic kidney cells (HEK 293 T) treated with tellurite show a partial inhibition of lipoamide dehydrogenase. In addition to the toxicological implications of tellurium compounds, the reported results suggest that tellurite and its derivatives can be used as potential tools for studying biochemical reactions.