Effects of time, temperature, and honey on Nosema apis (Microsporidia: Nosematidae), a parasite of the honeybee, Apis mellifera (Hymenoptera: Apidae).

Newly emerged adult bees were fed with Nosema apis spores subjected to various treatments, and their longevity, proportions of bees infected, and spores per bee recorded. Spores lost viability after 1, 3, or 6 months in active manuka or multifloral honey, after 3 days in multifloral honey, and after 21 days in water or sugar syrup at 33 degrees C. Air-dried spores lost viability after 3 or 5 days at 40 degrees, 45 degrees, or 49 degrees C. Increasing numbers of bees became infected with increasing doses of spores, regardless of their subsequent food (active manuka honey, thyme honey, or sugar syrup). Final spore loads were similar among bees receiving the same food, regardless of dose. Bees fed with either honey had lighter infections than those fed with syrup, but this may have been due to reductions in their longevity. Bees fed with manuka honey were significantly shorter lived, whether infected or not.     

The effects of turbulent jet flows on plant cell suspension cultures

Cell suspensions of Morinda citrifolia were subjected to turbulent flow conditions in a submerged jet apparatus, to investigate their hydrodynamic shear susceptibility. The suspensions were exposed to repeated, pressure-driven passages through a submerged jet. Two nozzles, of 1 mm and 2 mm diameter, were employed. Average energy dissipation rates were in the range 10(3)-10(5) W/kg and cumulative energy dissipation in the range 10(5)-10(7) J/m3. System response to the imposed conditions was evaluated in terms of suspension viability (determined using a dye exclusion technique) and variations in both chain length distribution and maximum chain length. Viability loss was well-described by a first-order model, and a linear relationship was identified between the specific death rate constant and the average energy dissipation rate. This relationship was consistent with results obtained using the same suspension cultures in a turbulent capillary flow device. Morphological measurements indicated that exposure to the hydrodynamic environment generated in the jet resulted in a significant reduction in both the average and maximum chain lengths, and the reduction in the maximum chain length was identified as an appropriate measure of sustained damage. Analysis of both viability and chain length in terms of cumulative energy dissipated revealed good agreement with results reported by other authors for morphologically different plant cell systems. Copyright 1998 John Wiley & Sons, Inc.     

Physiology and Growth of Wheat Across a Subambient Carbon Dioxide Gradient

Two cultivars of wheat (Triticum aestivum L.), 'Yaqui 54' and'Seri M82', were grown along a gradient of daytime carbon dioxideconcentrations ([CO₂]) from near 350-200 µmol CO₂ mol^-1air in a 38 m long controlled environment chamber. Carbon dioxidefluxes and evapotranspiration were measured for stands (plantsand soil) in five consecutive 7·6-m lengths of the chamberto determined potential effects of the glacial/interglacialincrease in atmospheric [CO₂] on C₃ plants. Growth rates andleaf areas of individual plants and net assimilation per unitleaf area and daily (24-h) net CO₂ accumulation of wheat standsrose with increasing [CO₂]. Daytime net assimilation (P_D, mmolCO₂ m^-2 soil surface area) and water use efficiency of wheatstands increased and the daily total of photosynthetic photonflux density required by stands for positive CO₂ accumulation(light compensation point) declined at higher [CO₂]. Nighttimerespiration (R_N, mmol CO₂ m^-2 soil surface) of wheat, measuredat 369-397 µmol mol^-1 CO₂, apparently was not alteredby growth at different daytime [CO₂], but R_N /P_D of stands declinedlinearly as daytime [CO₂] and P_D increased. The responses ofwheat to [CO₂], if representative of other C₃ species, suggestthat the 75-100% increase in [CO₂] since glaciation and the30% increase since 1800 reduced the minimum light and waterrequirements for growth and increased the productivity of C₃plants.Copyright 1993, 1999 Academic Press Atmospheric carbon dioxide, carbon accumulation, evapotranspiration, light compensation point, net assimilation, respiration, Triticum aestivum, water use efficiency, wheat     

Hotspots for generalized recombination in the Escherichia coli chromosome.

A naturally occurring hotspot for Rec recombination of Escherichia coli was located in the biotin operon. The phenotypes of the bio hotspot as observed in λbio transducing phage were identical to those of Chi mutations in phage λ. In addition to recA⁺ function, the site-specific stimulation of recombination required recB⁺ function. The stimulation took place when the hotspot was present in only one parent of the cross and even when present opposite a region of heterology.The demonstration of a Chi element in E. coli provoked us to measure the density of Chi elements on the chromosome. E. coli DNA sampled in λ transducing phage (either obtained by induction of secondary site lysogens or made in vitro from EcoRI cleavage fragments) showed one hotspot per 5 to 15 × 10³ bases. The high density and the fact that Chi stimulation of recombination can span the inter-Chi distance suggest that Chi might be important in Rec recombination in the absence of λ.     

Membrane-free scrapie activity.

Determinations of scrapie activity in subcellular fractions from infected hamster brains through the asymptomatic and symptomatic course of infection revealed the presence of substantial amounts of scrapie infectivity in the 100,000 X g supernatant fractions, indicating that association with physically discernible membrane structures is not necessary for the transmission of the scrapie agent. An increase of scrapie infectivity in the 100,000 X g supernatant fractions after vigorous homogenization of infected membrane-rich fractions suggests that the agent is identical in membrane-rich and 100,000 X g supernatant fractions.     

Activities of enzymes that metabolize platelet-activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) in neutrophils and eosinophils from humans and the effect of a calcium ionophore

Enzymatic systems in human blood cells are described for the activation and inactivation of a biologically active phospholipid (1-alkyl-2-acetyl-$\text{sn}$-glycero-3-phosphocholine) with hypotensive, platelet-aggregating, and inflammatory properties. The results document the presence of alkyldihydroxyacetone-phosphate synthase (forms the $\text{O}$-alkyl linkage in lipids), 1-alkyl-2-lyso-$\text{sn}$-glycero-3-phosphocholine:acetyl-CoA acetyltransferase (produces the biologically active molecule), and 1-alkyl-2-acetyl-$\text{sn}$-glycero-3-phosphocholine: acetylhydrolase (destroys the biological activity) in human neutrophils and eosinophils. Both the acetyltransferase and acetylhydrolase activities are increased severalfold after treatment of normal neutrophils with ionophore A23187; however, alkyldihydroxyacetone-phosphate synthase activity is not influenced by the ionophore. Eosinophils isolated from patients with eosinophilia have significantly greater activities of all the enzymes studied than the eosinophils isolated from normal individuals. Our results indicate the acetyltransferase responsible for 1-alkyl-2-acetyl-$\text{sn}$-glycero-3-phosphocholine synthesis may serve an important role in human blood cells that release this biologically active phospholipid. Moreover, the acetyltransferase activity was found to be dramatically influenced by calcium flux.     

An HLA-I signature favouring KIR-educated Natural Killer cells mediates immune control of HIV in children and contrasts with the HLA-B-restricted CD8+ T-cell-mediated immune control in adults

Natural Killer (NK) cells contribute to HIV control in adults, but HLA-B-mediated T-cell activity has a more substantial impact on disease outcome. However, the HLA-B molecules influencing immune control in adults have less impact on paediatric infection. To investigate the contribution NK cells make to immune control, we studied >300 children living with HIV followed over two decades in South Africa. In children, HLA-B alleles associated with adult protection or disease-susceptibility did not have significant effects, whereas Bw4 (p = 0.003) and low HLA-A expression (p = 0.002) alleles were strongly associated with immunological and viral control. In a comparator adult cohort, Bw4 and HLA-A expression contributions to HIV disease outcome were dwarfed by those of protective and disease-susceptible HLA-B molecules. We next investigated the immunophenotype and effector functions of NK cells in a subset of these children using flow cytometry. Slow progression and better plasma viraemic control were also associated with high frequencies of less terminally differentiated NKG2A+NKp46+CD56^dim NK cells strongly responsive to cytokine stimulation and linked with the immunogenetic signature identified. Future studies are indicated to determine whether this signature associated with immune control in early life directly facilitates functional cure in children.     

Characterization of a Pseudomonas putida Allylic Alcohol Dehydrogenase Induced by Growth on 2-Methyl-3-Buten-2-ol

We have been working to develop an enzymatic assay for the alcohol 2-methyl-3-buten-2-ol (232-MB), which is produced and emitted by certain pines. To this end we have isolated the soil bacterium Pseudomonas putida MB-1, which uses 232-MB as a sole carbon source. Strain MB-1 contains inducible 3-methyl-2-buten-1-ol (321-MB) and 3-methyl-2-buten-1-al dehydrogenases, suggesting that 232-MB is metabolized by isomerization to 321-MB followed by oxidation. 321-MB dehydrogenase was purified to near-homogeneity and found to be a tetramer (151 kDa) with a subunit mass of 37,700 Da. It catalyzes NAD⁺-dependent, reversible oxidation of 321-MB to 3-methyl-2-buten-1-al. The optimum pH for the oxidation reaction was 10.0, while that for the reduction reaction was 5.4. 321-MB dehydrogenase oxidized a wide variety of aliphatic and aromatic alcohols but exhibited the highest catalytic specificity with allylic or benzylic substrates, including 321-MB, 3-chloro-2-buten-1-ol, and 3-aminobenzyl alcohol. The N-terminal sequence of the enzyme contained a region of 64% identity with the TOL plasmid-encoded benzyl alcohol dehydrogenase of P. putida. The latter enzyme and the chromosomally encoded benzyl alcohol dehydrogenase of Acinetobacter calcoaceticus were also found to catalyze 321-MB oxidation. These findings suggest that 321-MB dehydrogenase and other bacterial benzyl alcohol dehydrogenases are broad-specificity allylic and benzylic alcohol dehydrogenases that, in conjunction with a 232-MB isomerase, might be useful in an enzyme-linked assay for 232-MB.     

Cell growth patterns in immobilization matrices

Within an immobilized cell matrix, mass transfer limitations on substrate delivery or product removal can often lead to a wide range of local chemical environments. As immobilized living cell populations actively grow and adapt to their surroundings, these mass transfer effects often lead to strong, time-dependent spatial variations in substrate concentration and biomass densities and growth rates. This review focuses on the methods that have been devised, both experimentally and theoretically, to study the non-uniform growth patterns that arise in the mass transfer limited environment of an immobilization matrix, with particular attention being paid to cell growth in polysaccharide gels.