The effects of fermentation conditions on yeast cell debris particle size distribution during high pressure homogenisation

Experiments were performed to characterize the particle size distribution of bakers' yeast cells during high pressure homogenisation. Results were obtained for mechanically agitated batch and continuously grown cultures under a range of operating conditions. It was found that the dependency of cell debris size distribution on the number of passes through the homogeniser and the homogeniser pressure was independent of the cell properties and culture conditions, but for a fixed pressure and number of passes the extent of disruption was strongly affected by the operating conditions in the fermenter. The entire cell debris size distributions were successfully simulated using the mean and variance of the distributions and a previously published model equation which related these parameters to the operating pressure and number of passes through the homogeniser.List of Symbols k breakage coefficient in Eq. 1 - d cell diameter - d ₅₀ median diameter of homogenate size distribution - d ₅₀ dimensionless d ₅₀ defined as - D dilution rate - F(d _NP) cumulative undersize distribution (volume basis) - N number of passes - P total pressure - P _threshold threshold pressure - P (P-P _threshold) - w Boltzmann parameter, Eq. 4 - w dimensionless standard deviation defined as Greek Letters exponent in Eq. 1 - exponent in Eq. 1 UCL is the Biotechnology and Biological Sciences Research Council's Interdisciplinary Research Centre for Biochemical Engineering and the Council's support to the participating UCL departments is gratefully acknowledged. The provision of continuous fermentation material from Dr. M. Gregory, Process System Engineering IRC, is gratefully acknowledged.     

The Effect of Abiotic Factors on the Male Mate Searching Behavior and the Mating Success of Aphidius ervi (Hymenoptera: Aphidiidae)

The effect of wind speed and distance from the source on the male response of the aphid parasitoid, Aphidius ervi (Hymenoptera: Aphidiidae), to a pheromone source was studied in a wind tunnel. The number of males taking flight, entering the plume and successfully reaching the source, decreased at wind speeds >50 cm/s. Furthermore, the proportion of those attempting upwind flight that fell to the ground increased with increasing wind speed. In contrast, distance from the source had no significant effect on any of the parameters examined. While male flight behavior was significantly reduced at 70 cm/s, some males walked to the source when there was a bridge connecting the pheromone source and the release platform. This suggests that ambulatory behavior could be a significant component of male mate searching in A. ervi when wind conditions are too strong for upwind flight. The possible effects of variation in atmospheric pressure on male flight behavior to the long distance pheromone, as well as to the short distance one, were also investigated. No significant effects of atmospheric pressure were observed. These findings differ significantly from those previously reported for another aphid parasitoid, A. nigripes, and the reasons for such differences are discussed.     

The interplay between colonization history and gene flow in passively dispersing zooplankton: microsatellite analysis of rotifer resting egg banks

Zooplanktonic organisms that disperse passively as diapausing eggs often exhibit surprisingly strong population subdivision given their high colonization ability. Here we attempt to disentangle the impacts of colonization history and gene flow on these organisms by studying the population genetic structure of the rotifer Brachionus plicatilis. The resting egg banks of B. plicatilis in fourteen salt lake populations in the Iberian Peninsula were examined using seven microsatellite loci. A remarkably high degree of geographical structuring was found (F_st=0.43), with a significant pattern of isolation by distance. Microsatellite loci were in genetic equilibrium, ruling out inbreeding as an important force in population structuring. Comparisons are drawn with previously published phylogeographical data. Surprisingly, introgression of nuclear genes was detected in neighbouring populations with divergent mtDNA haplotypes. These results stress the long lasting impact of colonization history and the modulating effect of gene flow at local scales in these organisms.     

Thermal deactivation affects disruption of Escherichia coli

Summary The effect of thermal deactivation on disruption efficiency and cell-debris size has been investigated for E. coli. Disruption for thermally-deactivated cells was substantially lower than for stationary cells. Cell-debris size was also larger. Thermal deactivation has a significant impact on subsequent downstream operations such as homogenisation and centrifugation.     

Insular biogeography of the montane butterfly faunas in the Great Basin: comparison with birds and mammals

Summary Butterfly species lists were assembled for 18 Great Basin mountain ranges for which distributional data on mammals and birds have been analysed previously by other workers. The ranges represent remnant islands of the boreal habitat that once was continuous across the Great Basin but is now restricted to higher elevations as a result of climatic change at the close of the Pleistocene. The effects of biogeographic factors (area, distance, elevation) and habitat diversity on butterfly species number were examined. The Great Basin boreal butterfly faunas were found to be depauperate overall relative that of the principal mainland source, the Rocky Mountains, and were found to have fewer species than predicted by the mainland species-area data. However, only a weak area effect, and no distance effect, was detected by bivariate and multivariate analysis. Furthermore, the habitat diversity score found to explain virtually all the variation in bird species number in the same ranges in previous studies is only marginally significantly correlated with butterflies. When the butterflies are subdivided according to their vagility, the relative differences in the species-area correlation and slope (z-value) between the vagility categories were consistent with those found previously for mammals and birds, and, as predicted by theory, less vagile taxa exhibit higher species-area correlations and z-values. Overall, differences in the insular biogeography of buttterflies and vertebrates seem to reflect fundamental ecological differences between the taxa.     

Physical and physiological costs of ectoparasitic mites on host flight endurance

1. Dispersal is essential for locating mates, new resources, and to escape unfavourable conditions. Parasitism can impact a host's ability to perform energetically demanding activities such as long‐distance flight, with important consequences for gene flow and meta‐population dynamics. 2. Ectoparasites, in particular, can adversely affect host flight performance by diminishing flight aerodynamics and/or by inflicting physiological damage while feeding on host tissue. 3. Experimental flight assays were conducted using two fruit fly‐mite systems: Drosophila nigrospiracula (Patterson and Wheeler) – Macrocheles subbadius (Berlese) and D. hydei (Sturtevan) – M. muscaedomesticae (Scopoli). Flies that are burdened by mites are expected to exhibit lower flight endurance compared to uninfected flies. 4. The results show that the presence of mites (attached) significantly decreased flight endurance by 57% and 78% compared to uninfected D. nigrospiracula and D. hydei, respectively. The physiological damage caused by M. subbadius was revealed through a 53% decline in flight time among previously infected flies (mites removed just prior to flight assay). Surprisingly, the presumably phoretic M. muscaedomesticae also caused a 62% reduction in flight endurance among previously infected D. hydei. 5. These results suggest a strong deleterious effect of ectoparasitic mites on host flight performance, mediated by a reduction in flight aerodynamics and damage to host physiology. Adverse effects on host flight and/or dispersal may have broad implications for gene flow, population genetic structure, and local adaptation in both host and parasite meta‐populations.     

Extending the range of FRET—the Monte Carlo study of the antenna effect

The problem of extending the utilizable range of Förster resonance energy transfer (FRET) is of great current interest, due to the demand of conformation studies of larger biological structures at distances exceeding typical limiting distance of 100 Å. One of the ways to address this issue is the use of so-called antenna effect. In the present work, the influence of the antenna effect on the FRET efficiency is investigated by the Monte Carlo analysis. The previously published results Bojarski et al. (J Phys Chem B 115:10120–10125, 2011) indicate that using a simple model of donor linked with a protein labeled with multiple acceptors, significantly increases the transfer efficiency in comparison with donor–single acceptor system. The effect is stronger if the transition moments of acceptors are mutually parallel. In this work, to extend the scope of possible biological systems to be analyzed, different distributions of donor–acceptors distance are analyzed, as well as the size and shape of the attached molecule.     

A matching procedure for sequential experiments that iteratively learns which covariates improve power

We propose a dynamic allocation procedure that increases power and efficiency when measuring an average treatment effect in sequential randomized trials exploiting some subjects' previous assessed responses. Subjects arrive sequentially and are either randomized or paired to a previously randomized subject and administered the alternate treatment. The pairing is made via a dynamic matching criterion that iteratively learns which specific covariates are important to the response. We develop estimators for the average treatment effect as well as an exact test. We illustrate our method's increase in efficiency and power over other allocation procedures in both simulated scenarios and a clinical trial dataset. An R package “SeqExpMatch ” for use by practitioners is available on CRAN .     

Host population genetics and biogeography structure the microbiome of the sponge Cliona delitrix

Sponges occur across diverse marine biomes and host internal microbial communities that can provide critical ecological functions. While strong patterns of host specificity have been observed consistently in sponge microbiomes, the precise ecological relationships between hosts and their symbiotic microbial communities remain to be fully delineated. In the current study, we investigate the relative roles of host population genetics and biogeography in structuring the microbial communities hosted by the excavating sponge Cliona delitrix. A total of 53 samples, previously used to demarcate the population genetic structure of C. delitrix, were selected from two locations in the Caribbean Sea and from eight locations across the reefs of Florida and the Bahamas. Microbial community diversity and composition were measured using Illumina‐based high‐throughput sequencing of the 16S rRNA V4 region and related to host population structure and geographic distribution. Most operational taxonomic units (OTUs) specific to Cliona delitrix microbiomes were rare, while other OTUs were shared with congeneric hosts. Across a large regional scale (>1,000 km), geographic distance was associated with considerable variability of the sponge microbiome, suggesting a distance–decay relationship, but little impact over smaller spatial scales (<300 km) was observed. Host population structure had a moderate effect on the structure of these microbial communities, regardless of geographic distance. These results support the interplay between geographic, environmental, and host factors as forces determining the community structure of microbiomes associated with C. delitrix. Moreover, these data suggest that the mechanisms of host regulation can be observed at the population genetic scale, prior to the onset of speciation.     

Little evidence of a road‐effect zone for nocturnal,flying insects

Roads and traffic may be contributing to global declines of insect populations. The ecological effects of roads often extend far into the surrounding habitat, over a distance known as the road‐effect zone. The quality of habitat in the road‐effect zone is generally degraded (e.g., due to edge effects, noise, light, and chemical pollution) and can be reflected in species presence, abundance, or demographic parameters. Road‐effect zones have been quantified for some vertebrate species but are yet to be quantified for insects. Investigating the road‐effect zone for insects will provide a better understanding of how roads impact ecosystems, which is particularly important given the role insects play as pollinators, predators, and prey for other species. We quantified the road‐effect zone for nocturnal flying insects along three major freeways in agricultural landscapes in southeast Australia. We collected insects using light traps at six points along 2‐km transects perpendicular to each highway (n = 17). We sorted the samples into order, and dried and weighed each order to obtain a measure of dry biomass. Using regression models within a Bayesian framework of inference, we estimated the change in biomass of each order with distance from the road, while accounting for environmental variables such as temperature, moon phase, and vegetation structure. The biomass of nine of the ten orders sampled did not change with distance from the freeway. Orthoptera (i.e., grasshoppers and crickets) was the only order whose biomass increased with distance from the freeway. From our findings, we suggest that the impacts of roads on insects are unlikely extending into the surrounding landscape over a distance of 2 km. Therefore, if there are impacts of roads on insects, these are more likely to be concentrated at the road itself, or on finer taxonomic scales such as family or genus level.     

Spectroscopic investigation of alloyed quantum dot‐based FRET to cresyl violet dye

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R₀, intermolecular distance (r) , rate of energy transfer k_T (r), and transfer efficiency (E) are determined by employing both steady‐state and time‐resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern–Volmer (K_D) and bimolecular quenching constants (k_q) are determined from the Stern–Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimation of transport distance of fine particulate organic matter in relation to channel morphology in tailwaters of the Lake Biwa and reservoir dams

Knowledge on transport and deposition of fine particulate organic matter (FPOM) from reservoir dams is increasingly required for habitat management and restoration of dam tailwater ecosystems. Variations in the transport distance of FPOM, however, have never been studied well, particularly in relation to channel morphology, due to channel size restrictions of artificial tracers such as corn pollen when applied to larger river channels. This study aims to show the relations between FPOM retention efficiency and channel morphology in dam tailwaters using lentic plankters as tracers. We estimated the mean transport distance, S _p, by calculating downstream reduction ratios of lentic tracer plankters and calculated the deposition velocity, v _dep. Suspended FPOM samples were collected in tailwaters of two river channels below reservoir dams and two artificial canals below Lake Biwa in the Yodo River system. The longest S _p (19.2 km) and the shortest one (2.2 km) were recorded in the deep canal and shallow canal, respectively, showing a positive correlation with channel hydraulic radius. The values of v _dep were 4.7–6.4 times higher in river channels than in artificial canals. These results indicate that increasing complexity of bed morphology can minimize S _p, whereas bed degradation and armored bed materials may lead to increased S _p. Advantages of lentic plankters as tracers for estimating distance ranges of reservoir dam impact on river ecosystems are also discussed.     

The impact of local spatial resistance on the movement behaviour of Tenebrio molitor L.

Although the impact of vegetation and other environmental factors on the distribution of terrestrial invertebrates has been known since the 1950s, basic knowledge about their interaction with micro-landscape elements is lacking. In experimental model systems, the impact of varying local spatial resistance (LSR) on the distribution of Tenebrio molitor individuals was analysed in the laboratory. In the setups, LSR led to a reduction of the average distance covered (move step length) and a reduction of the velocity (the maximum speed ranging from 36.1 in the control groups to 20.4 [mm*step⁻¹] in areas with a maximum LSR). Also, the covered distances per individual varied among three groups, from 2.97 m in the control to 1.11 m in areas with medium LSR to 0.88 m in areas with maximum LSR. Thus, in areas with LSR, animals were forced by their habitats to perform shorter move steps on average and covered less distance. The distance covered (i.e., dispersal performances) were not correlated with such factors as sex, weight and length of the Tenebrio individuals from other studies. Analysis of the data for net squared displacement indicated that the dispersal of the beetles did not follow a diffusion process. The move step directions of the dispersal data showed pronounced autocorrelation, which means that in contrast to other findings, the individuals were not performing a random walk. This effect was strongly dependent on the temporal resolution (i.e. grain), and was also influenced by the experimental conditions. The entire array of data showed high variability among the sub-groups (as well as many outliers), revealing nonparametric characteristics. The results showed that the specific physical configuration of suitable habitat for Tenebrio is one of the key indicators of landscape connectivity on the micro-scale.     

Failure to avoid rutin diets results in altered food utilization and reduced growth rate ofManduca sexta larvae

The possibility of avoidance of and dietary self-selection relative to the flavonol rutin was examined for third instarManduca sexta for two thermal regimes and for larvae previously reared on plain or rutin diet. Temperature affected all of the performance indices examined, except efficiency of conversion of digested food. Significant interactive effects between temperature and diet occurred for relative consumption rate, relative growth rate and the food utilization efficiencies. For example, at the warm daytime temperature, relative growth rate prior to head capsule slippage was lower for caterpillars previously reared on rutin diet compared to those reared on plain diet. In contrast, at the cool daytime temperature, the relative growth rates were similar for caterpillars reared on plain diet and on 6 μmoles rutin diet. Consequently, in some treatments (5 of 12), caterpillars with a history of rutin in their diet had lower relative growth rates than those experiencing rutin for the first time. Despite rutin's impact on food utilization indices and negative effect on relative growth rate, the caterpillars did not avoid rutin nor was there evidence of regulation of the intake of rutin. The lack of metabolic feedback is discussed.     

Short-Term Vegetation and Soil Responses to Mechanical Destruction of Rabbit (Oryctolagus cuniculus L.) Warrens in an Australian Box Woodland

We studied the impact of disturbance by rabbits on plants and soils along a gradient out from the center of ripped rabbit warrens in an Australian semiarid woodland. Five years after the warrens were ripped, the impact of rabbits was still apparent. The cover of bare soil declined, and the cryptogam cover increased with increasing distance from the warren mound. However, litter cover, plant cover, and plant diversity remained unchanged with increasing distance from the mounds. Differences in plant composition were apparent with increasing distance from the mounds, with three species, Schismus barbatus, Salsola kali var. kali, and Chenopodium melanocarpum dominating the mounds, whereas the perennial grass Austrostipa scabra dominated the nonwarren control surfaces. Two species, Crassula sieberana and S. barbatus, dominated the active soil seed bank on ripped warrens. The mounds had the lowest number of species in the soil seed bank, whereas the warren edge microsite had the greatest. Ripped and unripped warrens differed substantially in their complement of species, and ripped warrens contained an order of magnitude fewer active warren entrances compared with unripped warrens. Ripped warrens also had significantly more plant cover than unripped warrens. Taken together, our results reinforce the view that rabbits have a destructive effect on surface soils and vegetation in semiarid woodlands and suggest that restoration of the original woodland vegetation after warren ripping is likely to be a slow and ongoing process.     

Understanding the effect of tert-butanol on Candida antarctica lipase B using molecular dynamics simulations

The use of organic solvents as reaction media for enzymatic reactions has many advantages. Several organic solvents have been proposed as reaction media, especially for transesterifications using Candida antarctica lipase B (CalB). Among organic solvents, tert-butanol is associated with an enhanced conversion rate in bio-diesel production. Thus, it is necessary to understand the effect of tert-butanol on CalB to explain the high-catalytic efficiency compared with the reaction in other hydrophilic organic solvents. In this study, the effects of tert-butanol on the structure of CalB were investigated by MD simulations. The overall flexibility was increased in the presence of tert-butanol. The substrate entrance and the binding pocket size of CalB in tert-butanol were maintained as in TIP3P water. The distance between the catalytic residues of CalB in tert-butanol indicated a higher likelihood of forming hydrogen bonds. These structural analyses could be useful for understanding the effect of tert-butanol on lipase transesterification.     

Nonconsumptive effects of hunting on a nontarget game bird

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Shorter T-DNA or additional virulence genes improve Agrobactrium-mediated transformation

The effect of additional virulence (vir) genes and size of plasmid T-DNA in Agrobacterium tumefa- ciens was investigated for their impact on transformation efficiency. Transformation efficiency in tobacco, cotton, and rice was increased when the T-DNA was 4.3 kb compared to 8.4 kb in size. However, when additional virG, virGN54D,virE, or virE/virG plasmids were included with the 8.4-kb T-DNA, transformation frequencies in all cases were increased over that of the shorter T-DNA without additional vir plasmids. The use of virE, virG or virGN54D copies enhanced transformation efficiency; however, the most significant increase of transformation efficiency in all three plant species was observed when the virE/virG plasmid was used for infection. The virE/virG plasmid dramatically enhanced the efficiency of Agrobacterium-mediated gene transfer; moreover, this plasmid appears to have broad efficiency since it was consistently effective on two different dicotyledon species as well as a monocotyledon species. Received: 8 February 2000 / Accepted: 21 March 2000     

Spatial synchrony of prairie ducks: roles of wetland abundance, distance, and agricultural cover

Populations exhibit spatial synchrony when their numbers rise and fall in concert at several sites over their distribution. I examined the relationship between synchrony, abundance of wetlands (ponds), distance, and agricultural cover using count data of ten duck species counted in 23 aerial survey strata on the mid-continental prairies of North America. Expansion of agriculture may have resulted in increased synchrony of duck populations through increased foraging efficiency of nomadic predators and/or if the homogenization of nesting habitat has removed habitat features that allow differential local responses to large-scale population drivers such as precipitation. As a measure of synchrony, I calculated all pair-wise cross-correlation coefficients based on population growth rates (r _t ) at each survey stratum, and then regressed these correlation coefficients against measures of cross-correlation of pond (wetland) counts, distance between strata, and mean percent area of strata seeded to row crops. Synchrony for most species was most strongly related to synchrony of wetland availability among sites, and decreased with distance between sites. Synchrony of ducks that nest over water showed little effect of agricultural cover, whereas the effect of agricultural cover on synchrony of upland nesting ducks differed by species. Mobile large-bodied species showed evidence of increased synchrony due to agricultural cover, whereas smaller-bodied, more philopatric species showed evidence of decreased synchrony due to agricultural cover.     

Seston capture by Hydropsyche siltalai and the accuracy of capture efficiency estimates

1. Suspension feeding by caseless caddisfly larvae (Trichoptera) constitutes a major pathway for energy flow, and strongly influences productivity, in streams and rivers. 2. Consideration of the impact of these animals on lotic ecosystems has been strongly influenced by a single study investigating the efficiency of particle capture of nets built by one species of hydropsychid caddisfly. 3. Using water sampling techniques at appropriate spatial scales, and taking greater consideration of local hydrodynamics than previously, we examined the size‐frequency distribution of particles captured by the nets of Hydropsyche siltalai. Our results confirm that capture nets are selective in terms of particle size, and in addition suggest that this selectivity is for particles likely to provide the most energy. 4. By incorporating estimates of flow diversion around the nets of caseless caddisfly larvae, we show that capture efficiency (CE) is considerably higher than previously estimated, and conclude that more consideration of local hydrodynamics is needed to evaluate the efficiency of particle capture. 5. We use our results to postulate a mechanistic explanation for a recent example of interspecific facilitation, whereby a reduction of near‐bed velocities seen in single species monocultures leads to increased capture rates and local depletion of seston within the region of reduced velocity.