Acanthamoeba myosin-II minifilaments assemble on a millisecond time scale with rate constants greater than those expected for a diffusion limited reaction

We have shown previously that Acanthamoeba myosin-II minifilaments assemble by three successive dimerization steps, forming, progressively, monomers, antiparallel dimers, antiparallel tetramers, and finally the full size octameric minifilament (Sinard, J. H., Stafford, W. F., and Pollard, T. D. (1989) J. Cell Biol. 109, 1537-1548). In the current study, we investigate the kinetics of the assembly of these minifilaments, initiating assembly by the rapid dilution of salt in a stopped-flow light scattering apparatus. The majority of the reaction is completed within 50 ms and is greater than 90% completed within 1 s. Assembly data over a greater than 6-fold myosin concentration range can be fit using the successive dimerization mechanism with a single set of rate constants. Second order rate constants for the initial steps in the assembly reaction exceed 10(8) M-1 s-1, and equilibrium dissociation constants predict a very low critical concentration, consistent with previous data. Other possible assembly mechanisms do not adequately fit all of the available data. Filament disassembly at 300 mM KCl is even more rapid, and there is both an increase in the dissociation rate constants and a decrease in the association rate constants with increasing KCl. Aggregation of minifilaments induced by Mg2+ is much slower and takes many minutes to reach equilibrium.     

Six ways in which a foraging predator may encounter options with different variances

We consider the idea that foraging animals seek to achieve a certain threshold intake of food per day rather than maximising mean energy intake. Earlier experiments and theoretical work have shown that under these conditions animals should respond to variance in reward. We identify six possible sources of such variance and produce models for five of them (the sixth is already solved). These models describe (1) whether to feed in habitats possessing small or large prey, (2) whether to feed on clumped or dispersed prey, (3) which prey items to eat, (4) the effects of misidentification of prey selection, (5) whether to feed singly or join a flock and (6) when to move between patches when the travel time between them is variable. The results are often radically different from those of traditional models and we discuss their biological significance.     

Megalencephalic leukoencephalopathy with subcortical cysts; a founder effect in Israeli patients and a higher than expected carrier rate among Libyan Jews

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a progressive inherited neurological disorder characterized by macrocephaly, deterioration in motor functions and cerebellar ataxia. In Israel the disease is found in an increased frequency among Libyan Jews. The disease is caused by mutations in the MLC1 gene, which encodes a putative CNS membrane transporter. We describe three novel mutations (p.G59E, p.P92S, and 134_136insC) in seven MLC families. One of these mutations, p.G59E, was found in the vast majority of MLC patients in Israel. Screening of 200 normal Libyan Jewish individuals for the p.G59E mutation, revealed a carrier rate of 1/40 compared with an expected carrier rate of 1/81. Several explanations could account for this difference the most likely one is an admixture of the Libyan Jewish population.     

Increasing frequency of bite wounds with increasing population density in Eurasian badgers, Meles meles

Eurasian badgers sometimes live in territorial, mixed-sex groups; the adaptive significance of this is not understood, but members generally interact amicably. None the less, badgers occasionally fight and inflict sometimes severe wounds on one another. Based on 498 badger life histories, from first emergence as a cub until death, documented during a 10-year trapping study at Wytham Woods, Oxfordshire, U.K., the patterns and rates of bite wounding and consequential scarring were examined. Male badgers received more wounds and more severe wounds than did females. Wounding rates for both sexes increased significantly with age, and there was evidence that heavier individuals received most wounds. No seasonal pattern in wounding rates was apparent. During the study, the badger population size increased three-fold and wounding rates, particularly in males, showed a density-dependent increase. The rate of bite wounding increased with group size, and this increase was more marked among males than among females. Among males, but not females, the rate of bite wounding also increased with the number of badgers living in adjoining territories.     

Increasing elephantLoxodonta africana density is a more important driver of change in vegetation condition than rainfall

The impact of African elephantsLoxodonta africana Blumenbuch, 1797 on biodiversity is hotly debated in wildlife management circles with scientists polarised in their views. This polarisation is largely due to the individual experiences of researchers. We aimed to determine whether elephants or rainfall patterns drove changes in vegetation condition (Normalised Difference Vegetation Index; NDVI) by avoiding a site-specific approach and looking at the issue at a broader scale. We used published estimates of elephant population density from 30 sites and recorded the change in density from 1995–1999, from 1999–2002 and from 2002–2006. We also recorded the deviation of annual rainfall from the long-term mean for those periods. We modelled these variables against the change in NDVI between periods using mixed effects models. We found that elephants were more influential in driving change in vegetation condition than rainfall, and this also occurred at one of our individual test sites where long-term data were available (Kruger). Elephants and rainfall combined to drive change in vegetation condition at our other long-term test site (Amboseli). Management activities (fencing, water provision) may cause the differences between the two long-term study sites. Change in productivity driven by rainfall has ramifications for biodiversity, suggesting that elephant derived changes in vegetation productivity (NDVI) also impacts on biodiversity. Thus, this study supports previous findings from individual sites that elephants impact vegetation, however there is also a suggestion that these impacts may vary according to management actions.     

Sequences of primate insulin genes support the hypothesis of a slower rate of molecular evolution in humans and apes than in monkeys.

The chimpanzee and African green monkey insulin genes have been cloned and sequenced. These two sequences together with the previously reported sequences for the human and owl monkey insulin genes provide additional support for the hominoid-rate-slowdown hypothesis, i.e., a slower rate of nucleotide substitution in humans and apes than in monkeys. When these sequences and other primate sequences available for the relative-rate test were considered together, the substitution rate in the Old World monkey lineage was shown to be significantly higher than the rates in the human and chimpanzee lineages. This was true regardless of whether the eta-globin pseudogene was included in the analysis. Therefore, in contrast to the claim by Easteal, the hominoid-rate-slowdown is not unique to the eta-globin pseudogene but appears to be a rather general phenomenon. On average, the substitution rate at silent sites is about 1.5 times higher in the Old World monkey lineage than in the human and chimpanzee lineages.     

Increasing ovulation rate and lambing rate in sheep by treatment with a steroid enzyme inhibitor

Treatment of ewes with a 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) inhibitor (Epostane) resulted in a significant increase in both ovulation rate and in the mean number of lambs per ewe lambing. The progestagen sponge plus 3 beta-HSD inhibitor treatment also caused a significant increase in oestrous cycle duration of approximately 1.5 days. Treatment of ewes with the 3 beta-HSD inhibitor caused a significant decrease in peripheral progesterone concentrations, which were reduced even further when 3 beta-HSD inhibitor treatment was given to ewes after insertion of a progestagen sponge. However, mean oestradiol concentrations were significantly higher in the two treatment groups, both at the end of the luteal phase and during the follicular phase of the oestrous cycle. These results demonstrate that ovulation rate and the production of lambs per ewe lambing can be significantly increased by 3 beta-HSD inhibitor treatment.     

Increasing pulse wave velocity in a realistic cardiovascular model does not increase pulse pressure with age

The mechanism of the well-documented increase in aortic pulse pressure (PP) with age is disputed. Investigators assuming a classical windkessel model believe that increases in PP arise from decreases in total arterial compliance (C(tot)) and increases in total peripheral resistance (R(tot)) with age. Investigators assuming a more sophisticated pulse transmission model believe PP rises because increases in pulse wave velocity (c(ph)) make the reflected pressure wave arrive earlier, augmenting systolic pressure. It has recently been shown, however, that increases in c(ph) do not have a commensurate effect on the timing of the reflected wave. We therefore used a validated, large-scale, human arterial system model that includes realistic pulse wave transmission to determine whether increases in c(ph) cause increased PP with age. First, we made the realistic arterial system model age dependent by altering cardiac output (CO), R(tot), C(tot), and c(ph) to mimic the reported changes in these parameters from age 30 to 70. Then, c(ph) was theoretically maintained constant, while C(tot), R(tot), and CO were altered. The predicted increase in PP with age was similar to the observed increase in PP. In a complementary approach, C(tot), R(tot), and CO were theoretically maintained constant, and c(ph) was increased. The predicted increase in PP was negligible. We found that increases in c(ph) have a limited effect on the timing of the reflected wave but cause the system to degenerate into a windkessel. Changes in PP can therefore be attributed to a decrease in C(tot).     

Mutations in SID2, a novel gene in Saccharomyces cerevisiae, cause synthetic lethality with sic1 deletion and may cause a defect during S phase

SIC1 encodes a nonessential B-type cyclin/CDK inhibitor that functions at the G1/S transition and the exit from mitosis. To understand more completely the regulation of these transitions, mutations causing synthetic lethality with sic1 Delta were isolated. In this screen, we identified a novel gene, SID2, which encodes an essential protein that appears to be required for DNA replication or repair. sid2-1 sic1 Delta strains and sid2-21 temperature-sensitive strains arrest preanaphase as large-budded cells with a single nucleus, a short spindle, and an approximately 2C DNA content. RAD9, which is necessary for the DNA damage checkpoint, is required for the preanaphase arrest of sid2-1 sic1 Delta cells. Analysis of chromosomes in mutant sid2-21 cells by field inversion gel electrophoresis suggests the presence of replication forks and bubbles at the arrest. Deleting the two S phase cyclins, CLB5 and CLB6, substantially suppresses the sid2-1 sic1 Delta inviability, while stabilizing Clb5 protein exacerbates the defects of sid2-1 sic1 Delta cells. In synchronized sid2-1 mutant strains, the onset of replication appears normal, but completion of DNA synthesis is delayed. sid2-1 mutants are sensitive to hydroxyurea indicating that sid2-1 cells may suffer DNA damage that, when combined with additional insult, leads to a decrease in viability. Consistent with this hypothesis, sid2-1 rad9 cells are dead or very slow growing even when SIC1 is expressed.     

Fronts,jumps and secondary introductions suggested as different invasion patterns in marine species,with an increase in spread rates over time

Not all introduced (invasive) species in a region will spread from a single point of introduction. Long-distance dispersal or further introductions can obscure the pattern of spread, but the regional importance of such processes is difficult to gauge. These difficulties are further compounded when information on the multiple scale process of invasive species range expansion is reduced to one-dimensional estimates of spread (e.g. km yr⁻¹). We therefore compared the results of two different metrics of range expansion: maximum linear rate of spread and accumulation of occupied grid squares (50 × 50 km) over time. An analysis of records for 54 species of introduced marine macrophytes in the Mediterranean and northeast Atlantic revealed cases where the invasion process was probably missed (e.g. Atlantic Bonnemaisonia hamifera) and suggested cases of secondary introductions or erratic jump dispersal (Dasysiphonia sp. and Womersleyella setacea). A majority of species analysed showed evidence for an accumulation of invaded sites without a clear invasion front. Estimates of spread rate are increasing for more recent introductions. The increase is greater than can be accounted for by temporally varying search effort and implies a historical increase in vector efficiency and/or a decreased resistance of native communities to invasion.     

ApoE-containing high density lipoproteins and phospholipid transfer protein activity increase in patients with a systemic inflammatory response

High density lipoproteins (HDL) mediate reverse cholesterol transport as well as the clearance of oxidation products or inflammatory mediators, thereby contributing to tissue integrity. The decrease in HDL in inflammation has been attributed to decreased lecithin:cholesterol acyltransferase activity, whereas the role of phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein has not been analyzed in detail. We have studied the activities of HDL-modifying proteins and the heterogeneity of HDL in healthy control subjects and three groups of postsurgery patients: no bacterial infection (group 1), bacterial focus and systemic inflammatory response (group 2), and severe sepsis (group 3). For all patients, a decrease in total HDL could be demonstrated, with a loss of mainly large, apolipoprotein A-I (apoA-I) HDL particles, an almost total loss of apoC-I, and an increase in apoE HDL (200-500 kDa), which did not contain significant amounts of apoA-I, apoA-II, or apoC-I. PLTP activity was increased in patients of groups 2 and 3, paralleled by a redistribution of PLTP into a population of small (120- to 200-kDa) particles, probably representing PLTP homodimers or lipid-complexed PLTP.In summary, the increase in apoE HDL and PLTP activity may improve the delivery of energy substrates and phospholipids to tissues that must maintain cellular membrane homeostasis under conditions of inflammatory stress.     

Changes in phytoplankton over various time scales in a shallow, eutrophic: the Loch Leven experience with special reference to the influence of flushing rate

SUMMARY. 1. The pattern of fluctuations in the total biomass and species composition of phytoplankton in the shallow, eutrophic Loch Leven exhibits considerable inter-annual and within-year variability. Nevertheless, studies over the 18-year period reviewed here (1968–85) show that many of the observed changes can be explained in -terms of light regimes and the concentrations and fluxes of nutrients. On occasion, the incidence of fungal parasitism and of protozoan, rotiferan and crustacean grazing is also important. 2. Changes in annual mean algal biomass from very high levels in the late 1960s and early 1970s to somewhat lower levels in the late 1970s, followed by occasional high peaks in the present decade, are attributed to shifts in phosphorus loading-particularly from a P-rich industrial source. 3. In spite of complex and erratic sequences of algal species, seasonal patterns in the size distribution of the phytoplankton assemblage have been identified. However, these also changed. During the 4 years prior to 1971, Daphnia hyalina was not recorded in the plankton, and small algae have been abundant only in late winter or early spring. 4. The potential importance of the weather is highlighted as one of the possible causes of the irregular appearance of algal species. The effect of the characteristically variable, oceanicclimate of Northern Britain on this large (13.3 km²), shallow (z?= 3.9 m) loch is thought to be of particular importance. 5. The influence of the weather on phytoplankton sequences is explored by comparing records of monthly flushing rate values with time-series data on aspects of the aquatic environment and plankton populations. The preliminary assessment suggests that variation in flushing rate ( p ) has a considerable effect on temperature regimes and the supplies and in-loch dynamics of nutrients; through such changes, p controls major features of phytoplankton succession such as the temporal abundance of diatoms, as well as detailed sequences of events relating to the development and collapse of particular algal species - and. as a consequence, in some cases, of the animals preying on them. 6. Concluding remarks emphasize how little would have been understood about the functioning of shallow lakes, had the long-term commitment to Loch Leven research been abandoned. The view is also expressed that the findings are of considerably greater relevance to research on ‘classic’ stratifying lake systems, than the focus on the shallow waterbody might hitherto have suggested.     

High-resolution time series of vessel density in Kenyan mangrove trees reveal a link with climate

Tropical trees are often excluded from dendrochronological investigations because of a lack of distinct growth ring boundaries, causing a gap in paleoclimate reconstructions from tropical regions. The potential use of time series of vessel features (density, diameter, surface area and hydraulic conductivity) combined with spectral analysis as a proxy for environmental conditions in the mangrove Rhizophora mucronata was investigated. Intra-annual differences in the vessel features revealed a trade-off between hydraulic efficiency (large vessels) during the rainy season and hydraulic safety (small, more numerous vessels) during the dry season. In addition to the earlywood-latewood variations, a semiannual signal was discovered in the vessel density and diameters after Fourier transformation. The similarity in the Fourier spectra of the vessel features and the climate data, in particular mean relative humidity and precipitation, provides strong evidence for a climatic driving force for the intra-annual variability of the vessel features. The high-resolution approach used in this study, in combination with spectral analysis, may have great potential for the study of climate variability in tropical regions.     

Stomatal density responses of temperate woodland plants over the past seven decades of CO2 increase: a comparison of Salisbury (1927) with contemporary data

We investigated the possible effect of recent (1927-1995) increases in the concentration of atmospheric CO2 on the stomatal densities of leaves of a wide range of tree, shrub, and herb species (N = 60) by making new measurements for comparison with corresponding data reported by E. J. Salisbury in 1927--a time when ice core studies indicate CO2 concentrations ~55 mL/L lower than present. A detailed intraspecific study of the herb Mercurialis perennis showed plants of M. perennis in a Cambridgeshire woodland in 1994 had significantly lower stomatal densities, irrespective of leaf insertion point, compared with their 1927 counterparts. Comparisons made across species using evolutionary comparative methods (independent contrasts) revealed a significant (P 2 increases have influenced leaf morphology in a manner consistent with recent experiments and the palaeoecological record. Further analyses suggested that the strength of the stomatal density response was independent of life form but dependent on "exposure" and the initial leaf stomatal density. Consequently, firmer predictions for future changes in stomatal density across all species, expected as a possible result of anthropogenically related CO2 increases, may now be possible.     

Allosteric effects acting over a distance of 20-25 A in the Escherichia coli tryptophan synthase bienzyme complex increase ligand affinity and cause redistribution of covalent intermediates

The reactions of L-histidine (L-His) and L-tryptophan (L-Trp) with the alpha 2 beta 2 complex of Escherichia coli tryptophan synthase are introduced as probes both of beta-subunit catalysis and of ligand-mediated alpha-beta allosteric interactions. Binding of DL-alpha-glycerol 3-phosphate (GP), an analogue of 3-indole-D-glycerol 3'-phosphate (IGP), to the alpha-catalytic site increases the affinity of alpha 2 beta 2 for L-His 4.5-fold and the affinity for L-Trp 17-fold and brings about a redistribution of beta-bound intermediates that favors the quinonoids derived from each amino acid. Inorganic phosphate (Pi) (presumably via binding to the alpha-catalytic site) influences the distribution of L-His intermediates as does GP. Previous binding studies [Heyn, M. P., & Weischet, W. O. (1975) Biochemistry 14, 2962-2968] indicate that when the phosphoryl group subsite of the alpha-catalytic site is occupied by GP or Pi, a high-affinity indole subsite is induced at the alpha-catalytic site. Interaction of benzimidazole (BZ), an analogue of indole, with this site also shifts the distribution of beta-bound L-His intermediates in favor of the L-His quinonoid. In the absence of Pi or GP, BZ interacts primarily at the beta-catalytic site and competes with L-His for the beta-subunit indole subsite. Since L-His and GP (or Pi) are substrate analogues and L-Trp is the physiological product, these allosteric effects likely take place with the natural substrates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maintaining social cohesion is a more important determinant of patch residence time than maximizing food intake rate in a group-living primate,Japanese macaque (Macaca fuscata)

Animals have been assumed to employ an optimal foraging strategy (e.g., rate-maximizing strategy). In patchy food environments, intake rate within patches is positively correlated with patch quality, and declines as patches are depleted through consumption. This causes patch-leaving and determines patch residence time. In group-foraging situations, patch residence times are also affected by patch sharing. Optimal patch models for groups predict that patch residence times decrease as the number of co-feeding animals increases because of accelerated patch depletion. However, group members often depart patches without patch depletion, and their patch residence time deviates from patch models. It has been pointed out that patch residence time is also influenced by maintaining social proximity with others among group-living animals. In this study, the effects of maintaining social cohesion and that of rate-maximizing strategy on patch residence time were examined in Japanese macaques (Macaca fuscata). I hypothesized that foragers give up patches to remain in the proximity of their troop members. On the other hand, foragers may stay for a relatively long period when they do not have to abandon patches to follow the troop. In this study, intake rate and foraging effort (i.e., movement) did not change during patch residency. Macaques maintained their intake rate with only a little foraging effort. Therefore, the patches were assumed to be undepleted during patch residency. Further, patch residence time was affected by patch-leaving to maintain social proximity, but not by the intake rate. Macaques tended to stay in patches for short periods when they needed to give up patches for social proximity, and remained for long periods when they did not need to leave to keep social proximity. Patch-leaving and patch residence time that prioritize the maintenance of social cohesion may be a behavioral pattern in group-living primates.     

Population dynamics of Trichostrongylus colubriformis in sheep: model to predict the worm population over time as a function of infection rate and host age

The developing immunity of sheep to Trichostrongylus colubriformis infections was described by a mathematical function. The rate of adult establishment was assumed to be a measure of the host's acquired immunity to this parasite. Prediction of establishment from infection rate and host age was used to estimate worm burden, worm rejection and arrested development.     

Nickel in soil and maize plants grown on an oxisol treated over a long time with sewage sludge

Abstract

The major limitation for the use of sewage sludge in agriculture is the risk of soil contamination with heavy metals, and their possible transference to man via the food chain. The objective of this study was to evaluate the content of nickel (Ni) in soil by the two methods of digestion (HNO₃ + H₂O₂ + HCl and HClO₄ + HF), and in different parts of maize plants grown on a tropical soil classified as Typic Eutrorthox, that had been treated with sewage sludge for nine consecutive years, and the effects on dry matter and grain production. The experiment was carried out under field conditions in Jaboticabal-SP, using a randomized block design with four treatments and five replicates. Treatments consisted of: 0.0 (control, mineral fertilization), 45.0, 90.0 and 127.5t ha^?1 sewage sludge (dry basis), accumulated during nine years. Sewage sludge was manually applied to the soil and incorporated at 0.1 m depth before sowing the maize. Soil Ni evaluated by Jackson’s method was 76.8% higher than evaluated by the United States Environmental Protection Agency method that digests the samples by heating with concentrated HNO³, H²O² and HCl. Sewage sludge rates did not affect Ni content in the soil. Ni was accumulated in leaf and stem but was not detected in grain. Sewage sludge and mineral fertilization applied to soil for a long time caused similar effects on dry matter and grain production.