Effect of complex nitrogen sources on the production of penicillin acylase byBacillus megaterium

The following complex nitrogen sources were evaluated for the production of penicillin acylase byBacillus megaterium: casein hydrolysate, corn steep liquor, stick water concentrate, blood meal and defatted sunflower meal. Experiments were run in shake flasks at 30‡C and pH 7.0. Best results were obtained with casein hydrolysate: 244 IU/I were produced with a productivity of 20.3 IU/l/h and yield of 717.6 IU/g of nitrogen. The lowest results correspond to sunflower meal with 39 IU/1.     

Diurnal growth trends, water potential, and osmotic adjustment of maize and sorghum leaves in the field

The daily cycle of leaf elongation rate, water potential, and solute potential of maize and sorghum, as well as temperature, were monitored in the field. Major climatic features were high radiation and a minimum air temperature of about 12 C. Leaf elongation of both crops was slowest at night, presumably because of low temperature. Peak elongation rates were in daytime when leaf water potential (Ψ) was low. Solute potential also decreased during daylight, thus permitting the maintenance of appreciable turgor pressure, a critical parameter for cell expansion.     

The glucose transport activity of human erythrocyte membranes. Reconstitution in phospholipid liposomes and fractionation by molecular sieve and ion exchange chromatography

Human erythrocyte membranes, at a protein concentration of 1–2 g/l, were solubilized with 0.12 M cholate in the presence of 0.06 M phospholipid (egg yolk phospholipids or phosphatidylcholine). More than 40% of the protein was solubilized. Cholate was removed by molecular sieve chromatography, whereby liposomes formed. These liposomes exchanged D-glucose faster than L-glucose. The recovery of glucose transport activity in the reconstituted system was estimated to be higher than 16%.The liposomes were heterogeneous in size, as shown by molecular sieve chromatography on Sepharose 4B, and small liposomes predominated. In liposomes formed with phosphatidylcholine, the distribution of glucose transport activity did not parallel the distribution of protein or phospholipid, and the activity was found mainly in the smallest liposomes. The proteins were incorporated mainly into the liposomes that eluted at the lowest ionic strength upon ion exchange chromatography.The glucose transport activity separated into three main peaks upon ion exchange chromatography of egg yolk phospholipid liposomes. The activity eluted at low ionic strength. The liposomes contained proteins mainly from the 3- and 4.5-regions (nomenclature according to Steck, T.L. (1974) J. Cell Biol. 62, 1–19). The activity peaks were highest in the first part of the chromatogram. The protein distribution did not coincide with the variation in activity over each peak. Therefore, it cannot be excluded that a minor component not seen in the electrophoretic analyses might be responsible for the glucose transport activity.     

Calcium Regulation of Agonist Binding to α7-Type Nicotinic Acetylcholine Receptors in Adult and Fetal Rat Hippocampus

Abstract: Quantitative autoradiography was used to compare the binding properties of α7-type nicotinic acetylcholine receptors in fetal and adult rat hippocampus. Whereas there were high levels of ¹²⁵I-α-bungarotoxin (¹²⁵I-α-BTX) binding throughout fetal hippocampal field CA1, there was a significant decrease in binding site density in the adult. The affinity of ¹²⁵I-α-BTX binding, as well as α-cobratoxin and nicotine potency to displace ¹²⁵I-α-BTX, did not change with age. Addition of Ca²⁺ to the assay buffer did not alter ¹²⁵I-α-BTX binding, or α-cobratoxin inhibition of ¹²⁵I-α-BTX binding, although it significantly increased nicotine affinity at both ages. The effect of Ca²⁺ on agonist affinity was dose-dependent, with an EC₅₀ value of 0.25–0.5 m M . Ca²⁺ also significantly increased the cooperativity of nicotine displacement curves in stratum oriens of the adult, but not in the fetus. These findings indicate that the properties of hippocampal ¹²⁵I-α-BTX binding sites are largely similar across age. Ca²⁺ selectively enhances the affinity of agonist binding, with no change in antagonist binding. This ionic effect may result from potentiation of agonist binding to a desensitized state of the α7 nicotinic acetylcholine receptor and may represent an important neuroprotective mechanism.     

Sequence mapping in a three-dimensional space by a numeric method and some of its applications

In this work we report a simple way to assign a single numeric value in a three-dimensional space to a given nucleotide sequence. The method reported allows for theoretical comparisons of naturally occurring nucleotide sequences.     

Evidence of the importance of host habitat use in predicting the dilution effect of wild boar for deer exposure to Anaplasma spp

Foci of tick-borne pathogens occur at fine spatial scales, and depend upon a complex arrangement of factors involving climate, host abundance and landscape composition. It has been proposed that the presence of hosts that support tick feeding but not pathogen multiplication may dilute the transmission of the pathogen. However, models need to consider the spatial component to adequately explain how hosts, ticks and pathogens are distributed into the landscape. In this study, a novel, lattice-derived, behavior-based, spatially-explicit model was developed to test how changes in the assumed perception of different landscape elements affect the outcome of the connectivity between patches and therefore the dilution effect. The objective of this study was to explain changes in the exposure rate (ER) of red deer to Anaplasma spp. under different configurations of suitable habitat and landscape fragmentation in the presence of variable densities of the potentially diluting host, wild boar. The model showed that the increase in habitat fragmentation had a deep impact on Habitat Sharing Ratio (HSR), a parameter describing the amount of habitat shared by red deer and wild boar, weighted by the probability of the animals to remain together in the same patch (according to movement rules), the density of ticks and the density of animals at a given vegetation patch, and decreased the dilution effect of wild boar on deer Anaplasma ER. The model was validated with data collected on deer, wild boar and tick densities, climate, landscape composition, host vegetation preferences and deer seropositivity to Anaplasma spp. (as a measure of ER) in 10 study sites in Spain. However, although conditions were appropriate for a dilution effect, empirical results did not show a decrease in deer ER in sites with high wild boar densities. The model showed that the HSR was the most effective parameter to explain the absence of the dilution effect. These results suggest that host habitat usage may weaken the predicted dilution effect for tick-borne pathogens and emphasize the importance of the perceptual capabilities of different hosts in different landscapes and habitat fragmentation conditions for predictions of dilution effects.     

Optimization of human interferon gamma production in <Emphasis Type="Italic">Escherichia coli</Emphasis> by response surface methodology

The production of human interferon gamma (hIFN-γ) using a synthetic gene in Escherichia coli BL21-SI was optimized by response surface methodology (RSM) and a Box-Behnken design. The process variables studied were temperature, bio-mass concentration at induction time and the NaCl concentration as inducer. According to the Box-Behnken design, a second order response function was developed. The optimal expression conditions were a temperature of 32.6°C, induction biomass of 0.31 g/L and 0.3 M NaCl in minimal medium. The model prediction for the maximum hIFN-γ production was 77.3 mg/L, which corresponded satisfactorily with the experimental data. The hIFN-γ concentration attained under optimized conditions was 13-times higher than that obtained using the non-optimized conditions. We conclude that RSM is an effective method for the optimization of recombinant protein expression using synthetic genes in E. coli.     

Effects of substrate on interactions between juvenile sea scallops (Placopecten magellanicus Gmelin) and predatory sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say)

We investigated the effect of substrate (glass bottom, sand, granule, pebble) on predation of juvenile sea scallops (Placopecten magellanicus) by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) at two prey sizes (11-15 mm and 24-28 mm shell height), and two prey densities (10 and 30 scallops per aquarium) in laboratory experiments. Specifically, we quantified predation rate and underlying behaviours (proportion of time a predator spent searching for and handling prey, encounter rate between predators and prey, and various outcomes of encounters). We detected a significant gradual effect of particle size of natural substrates on sea star predation: specifically, predation rate on and encounter rate with small scallops tended to decrease with increasing particle size (being highest for sand, intermediate for granule, and lowest for pebble). Substrate type did not significantly affect predation rates or behaviours of sea stars preying on large scallops or of rock crabs preying on either scallop size classes. Other factors, such as prey size and density, were important in the scallop-sea star and scallop-rock crab systems. For example, predation rate by sea stars and crabs and certain sea star behaviours (e.g. probability of consuming scallops upon capture) were significantly higher with small scallops than with large scallops. As well, in interactions between small scallops and sea stars, predation rate and encounter rate increased with prey density, and the proportion of time sea stars spent searching was higher at low prey density than high prey density. Thus, substrate type may be a minor factor determining predation risk of seeded scallops during enhancement operations; prey size and prey density may play a more important role. However, substrate type still needs to be considered when choosing a site for scallop enhancement, as it may affect other scallop behaviours (such as movement).