Core-shell encapsulation formulations to stabilize desiccated Bradyrhizobium against high environmental temperature and humidity

Engineered materials to improve the shelf-life of desiccated microbial strains are needed for cost-effective bioaugmentation strategies. High temperatures and humidity of legume-growing regions challenge long-term cell stabilization at the desiccated state. A thermostable xeroprotectant core and hydrophobic water vapour barrier shell encapsulation technique was developed to protect desiccated cells from the environment. A trehalose core matrix increased the stability of desiccated Bradyrhizobium by three orders of magnitude over 20 days at 32°C and 50% relative humidity (RH) compared to buffer alone; however, the improvement was not deemed sufficient for a shelf-stable bioproduct. We tested common additives (skim milk, albumin, gelatin and dextran) to increase the glass transition temperature of the desiccated product to provide further stabilization. Albumin increased the glass transition temperature of the trehalose-based core by 40°C and stabilized desiccated Bradyrhizobium for 4 months during storage at high temperature (32°C) and moderate humidity (50% RH) with only 1 log loss of viability. Although the albumin-trehalose core provided exceptional protection against high temperature, it was ineffective at higher humidity conditions (75%). We therefore incorporated a paraffin shell, which protected desiccated cells against 75% RH providing proof of concept that core and shell encapsulation is an effective strategy to stabilize desiccated cells.     

Exogenous arachidonic acid mediates permeability of human brain microvessel endothelial cells through prostaglandin E2 activation of EP3 and EP4 receptors

The blood–brain barrier, formed by microvessel endothelial cells, is the restrictive barrier between the brain parenchyma and the circulating blood. Arachidonic acid (ARA; 5,8,11,14‐cis‐eicosatetraenoic acid) is a conditionally essential polyunsaturated fatty acid [20:4(n ? 6)] and is a major constituent of brain lipids. The current study examined the transport processes for ARA in confluent monolayers of human brain microvascular endothelial cells (HBMEC). Addition of radioactive ARA to the apical compartment of HBMEC cultured on Transwell^® inserts resulted in rapid incorporation of radioactivity into the basolateral medium. Knock down of fatty acid transport proteins did not alter ARA passage into the basolateral medium as a result of the rapid generation of prostaglandin E₂ (PGE₂), an eicosanoid known to facilitate opening of the blood–brain barrier. Permeability following ARA or PGE₂ exposure was confirmed by an increased movement of fluorescein‐labeled dextran from apical to basolateral medium. ARA‐mediated permeability was attenuated by specific cyclooxygenase‐2 inhibitors. EP₃ and EP₄ receptor antagonists attenuated the ARA‐mediated permeability of HBMEC. The results indicate that ARA increases permeability of HBMEC monolayers likely via increased production of PGE₂ which acts upon EP₃ and EP₄ receptors to mediate permeability. These observations may explain the rapid influx of ARA into the brain previously observed upon plasma infusion with ARA.

     

Early detection of Agrilus planipennis: investigations into the attractive range of the sex pheromone (3Z)-lactone

The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a highly destructive primary pest of ash (Fraxinus sp., Oleaceae) trees outside of its native range. Ash is an important component of many ecosystems and its loss would be detrimental to both the economy and the environment. The present study aimed to improve our understanding of the effectiveness of green sticky prism traps baited with host kairomone and insect pheromone lures for A. planipennis and to collect data for modelling the range of attraction of the pheromone (3Z)-dodecen-12-olide [(3Z)-lactone]. Traps were deployed over a single flight season in urban locations of Ontario, Canada, with low densities of EAB. Traps were placed in pairs of trees separated by not more than 25 m. All traps contained the host kairomone, (3Z)-hexenol, with the remaining half in each pairing additionally baited with (3Z)-lactone pheromone. Both lure types were highly effective in capturing EAB, with >90% detection rates overall. However, traps baited with the lactone pheromone and host volatile lures doubled trap captures of EAB over distances of at least 25 m from the nearest traps baited with only host volatiles. Although the baseline detection rate of traps containing (3Z)-hexenol alone is not significantly reduced compared with traps containing (3Z)-lactone, the overall trap effectiveness is significantly increased when (3Z)-lactone is present. The implications for the use of (3Z)-lactone at 3 mg per septum dose in an early warning trapping system are discussed. Trap layout methods and risk-based analysis models can now be further refined by including these data about the attractive range of lures and their behaviour in different plot environments.     

Microbial composition affects the functioning of estuarine sediments

Although microorganisms largely drive many ecosystem processes, the relationship between microbial composition and their functioning remains unclear. To tease apart the effects of composition and the environment directly, microbial composition must be manipulated and maintained, ideally in a natural ecosystem. In this study, we aimed to test whether variability in microbial composition affects functional processes in a field setting, by reciprocally transplanting riverbed sediments between low- and high-salinity locations along the Nonesuch River (Maine, USA). We placed the sediments into microbial ‘cages'' to prevent the migration of microorganisms, while allowing the sediments to experience the abiotic conditions of the surroundings. We performed two experiments, short- (1 week) and long-term (7 weeks) reciprocal transplants, after which we assayed a variety of functional processes in the cages. In both experiments, we examined the composition of bacteria generally (targeting the 16S rDNA gene) and sulfate-reducing bacteria (SRB) specifically (targeting the dsrAB gene) using terminal restriction fragment length polymorphism (T-RFLP). In the short-term experiment, sediment processes (CO₂ production, CH₄ flux, nitrification and enzyme activities) depended on both the sediment''s origin (reflecting differences in microbial composition between salt and freshwater sediments) and the surrounding environment. In the long-term experiment, general bacterial composition (but not SRB composition) shifted in response to their new environment, and this composition was significantly correlated with sediment functioning. Further, sediment origin had a diminished effect, relative to the short-term experiment, on sediment processes. Overall, this study provides direct evidence that microbial composition directly affects functional processes in these sediments.     

Diminished transmission of drug resistant HIV-1 variants with reduced replication capacity in a human transmission model

Background

Different patterns of drug resistance are observed in treated and therapy naïve HIV-1 infected populations. Especially the NRTI-related M184I/V variants, which are among the most frequently encountered mutations in treated patients, are underrepresented in the antiretroviral naïve population. M184I/V mutations are known to have a profound effect on viral replication and tend to revert over time in the new host. However it is debated whether a diminished transmission efficacy of HIV variants with a reduced replication capacity can also contribute to the observed discrepancy in genotypic patterns.As dendritic cells (DCs) play a pivotal role in HIV-1 transmission, we used a model containing primary human Langerhans cells (LCs) and DCs to compare the transmission efficacy M184 variants (HIV-M184V/I/T) to HIV wild type (HIV-WT). As control, we used HIV harboring the NNRTI mutation K103N (HIV-K103N) which has a minor effect on replication and is found at a similar prevalence in treated and untreated individuals.

Results

In comparison to HIV-WT, the HIV-M184 variants were less efficiently transmitted to CCR5⁺ Jurkat T cells by both LCs and DCs. The transmission rate of HIV-K103N was slightly reduced to HIV-WT in LCs and even higher than HIV-WT in DCs. Replication experiments in CCR5⁺ Jurkat T cells revealed no apparent differences in replication capacity between the mutant viruses and HIV-WT. However, viral replication in LCs and DCs was in concordance with the transmission results; replication by the HIV-M184 variants was lower than replication by HIV-WT, and the level of replication of HIV-K103N was intermediate for LCs and higher than HIV-WT for DCs.

Conclusions

Our data demonstrate that drug resistant M184-variants display a reduced replication capacity in LCs and DCs which directly impairs their transmission efficacy. As such, diminished transmission efficacy may contribute to the lower prevalence of drug resistant variants in therapy naive individuals.

     

Effect of dietary supplementation with a fish oil concentrate on the alkenylacyl class of ethanolamine phospholipid in human platelets

It has been demonstrated that the alkenylacyl class of ethanolamine phospholipid (PE) represents one of the major forms of eicosapentaenoic acid (EPA)-containing phospholipid in the circulating platelets isolated from human subjects consuming a fish oil concentrate. Since the alkenylacyl PE from human platelets is enriched in the eicosanoid precursor arachidonic acid (AA) and the n-6 polyunsaturate adrenic acid (AdA), it was of interest to study changes in alkenylacyl PE fatty acid composition upon fish oil supplementation. Healthy volunteers were given 20 capsules of MaxEPA daily (3.6 g of EPA plus 2.4 g of docosahexaenoic acid, DHA) for 6 weeks followed by a 6-week recovery period. Washed platelet suspensions were prepared and the fatty acid compositions of the phospholipid components were evaluated by thin-layer and gas-liquid chromatography at weeks 0, 3, 6, 9, and 12. Fatty acid composition changes were more pronounced in the alkenylacyl PE than in other platelet phospholipids as a result of fish oil consumption. The alkenylacyl PE exhibited a greater drop (by 20.3 mol%, i.e., from 72.0 to 51.7 mol%) in AA than diacyl PE (by 1.6 mol%) or total (predominantly diacyl) choline phospholipids (PC) (by 4.5 mol%). In alkenylacyl PE, the predominant reservoir of AdA in human platelet phospholipid, a dramatic reduction in the level of AdA also resulted with MaxEPA supplementation (from 7.9 to 3.1 mol%); diacyl PE and total PC decreased by 0.6 and 0.3 mol%, respectively. With respect to the n-3 fatty acids, EPA rose by 12.5 mol% in alkenylacyl PE, compared to only 3.8 and 2.5 mol% in diacyl PE and total PC, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of warmer winters on the demography of an outbreak insect is hidden by intraspecific competition

Warmer climates are predicted to increase bark beetle outbreak frequency, severity, and range. Even in favorable climates, however, outbreaks can decelerate due to resource limitation, which necessitates the inclusion of competition for limited resources in analyses of climatic effects on populations. We evaluated several hypotheses of how climate impacts mountain pine beetle reproduction using an extensive 9‐year dataset, in which nearly 10,000 trees were sampled across a region of approximately 90,000 km², that was recently invaded by the mountain pine beetle in Alberta, Canada. Our analysis supports the hypothesis of a positive effect of warmer winter temperatures on mountain pine beetle overwinter survival and provides evidence that the increasing trend in minimum winter temperatures over time in North America is an important driver of increased mountain pine beetle reproduction across the region. Although we demonstrate a consistent effect of warmer minimum winter temperatures on mountain pine beetle reproductive rates that is evident at the landscape and regional scales, this effect is overwhelmed by the effect of competition for resources within trees at the site level. Our results suggest that detection of the effects of a warming climate on bark beetle populations at small spatial scales may be difficult without accounting for negative density dependence due to competition for resources.     

Can chemical communication be cryptic? Adaptations by herbivores to natural enemies exploiting prey semiochemistry

Predators and parasites commonly use chemical cues associated with herbivore feeding and reproduction to locate prey. However, we currently know little about mechanisms by which herbivores may avoid such natural enemies. Pheromones are crucial to many aspects of herbivore life history, so radical alterations of these compounds could be disadvantageous despite their exploitation by predators. Instead, minor modifications in pheromone chemistry may facilitate partial escape while maintaining intraspecific functionality. We tested this hypothesis using Ips pini, an endophytic beetle that develops in the phloem tissue of pine trees. Its predominant predators in the Great Lakes region of North America are Thanasimus dubius and Platysoma cylindrica, both of which are highly attracted to I. pini’s pheromones. However, there are significant disparities between prey and predator behaviors that relate to nuances of pheromone chemistry. Thanasimus dubius is most attracted to the (+) stereoisomer of ipsdienol, and P. cylindrica is most attracted to the (−) form; Ips pini prefers racemic mixtures intermediate between each predator’s preferences. Further, a component that is inactive by itself, lanierone, greatly synergizes the attraction of I. pini to ipsdienol, but has a weak or no effect on its predators. A temporal component adds to this behavioral disparity: lanierone is most important in the communication of I. pini during periods when its predators are most abundant. The difficulties involved in tracking prey are further compounded by spatial and temporal variation in prey signaling on a local scale. For example, the preferences of I. pini vary significantly among sites only 50 km apart. This chemical crypsis is analogous to morphological forms of camouflage, such as color and mimicry, that are widely recognized as evasive adaptations against visually searching predators. Presumably these relationships are dynamic, with predators and prey shifting responses in microevolutionary time. However, several factors may delay predator counter adaptations. The most important appears to be the availability of alternate prey, specifically I. grandicollis, whose pheromone ipsenol is highly attractive to the above predators but not cross-attractive with I. pini. Consistent with this view, the specialist parasitoid, Tomicobia tibialis, has behavioral preferences for pheromone components that closely correspond with those of I. pini. These results are discussed in terms of population dynamics and coevolutionary theory. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

COX-2 expression in cystic kidneys is dependent on dietary n-3 fatty acid composition

Dietary n-3 fatty acids generally attenuate elevated cyclooxygenase-2 (COX-2) levels in disease states. However, models of renal cystic disease (RCD) exhibit reduced renal COX-2 expression. Therefore, the in vivo regulation of COX-2 expression by dietary n-3 fatty acids was examined. In archived tissues from dietary studies, COX-2 protein and gene expression was up-regulated in diseased pcy mouse and Han:SPRD-cy rat kidneys when given diets containing eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA), but not those containing -linolenic acid (ALA), compared to control diets with linoleic acid (LA). The presence of disease was necessary to elicit these effects as COX-2 expression was unaltered by diet in normal kidneys. The effects were specific for COX-2, since COX-1 levels were unaltered by these dietary manipulations in either model. Thus, in RCD, diets containing EPA and DHA but not ALA appear to specifically up-regulate renal COX-2 gene and protein levels in vivo.     

Gender- and sequence-dependent predation within group colonizers of defended plants: a constraint on cheating among bark beetles?

Bark beetles engage in one of the most pronounced examples of group procurement of defended plants. Their aggregation pheromones attract both sexes and are essential to overcome constitutive and rapidly inducible lethal defenses. The relative benefits to senders versus receivers of these signals are only partly understood. Because the initial stage of host entry can be hazardous, there may be benefit to a cheating strategy, whose practitioners respond to pheromones but do not engage in host searching. Several disadvantages to cheating have been proposed, but the role of predators has not been considered. Predators exploit bark beetle pheromones to locate prey, accumulate at the breeding site, and consume adult bark beetles before they enter the tree. Preliminary experiments quantified arrival patterns in the field. We used a laboratory assay to investigate relative predation on pioneers (those that initially select and enter hosts) and responders (those that arrive at a host in response to pheromones) during host colonization. Our model system utilized the pine engraver, Ips pini, which exhibits male harem polygamy. We allowed male I. pini to colonize host tissue and added females 1 day later. Also 1 day later, we variably added additional males and predacious checkered beetles, Thanasimus dubius. These treatments included two densities of males and three densities of predators that were selected to emulate field conditions. Responding males experienced higher predation than pioneers. T. dubius ate more males than females, independent of the presence or absence of responding males. T. dubius affected the distribution of females per male, although the number of females that survived to construct ovipositional galleries was constant. We discuss the viability of cheating, implications for biological control, and predator-prey coevolution in this cooperative, group-colonizing herbivore.