Mobile elements create strain-level variation in the services conferred by an aphid symbiont

Heritable, facultative symbionts are common in arthropods, often functioning in host defence. Despite moderately reduced genomes, facultative symbionts retain evolutionary potential through mobile genetic elements (MGEs). MGEs form the primary basis of strain-level variation in genome content and architecture, and often correlate with variability in symbiont-mediated phenotypes. In pea aphids (Acyrthosiphon pisum), strain-level variation in the type of toxin-encoding bacteriophages (APSEs) carried by the bacterium Hamiltonella defensa correlates with strength of defence against parasitoids. However, co-inheritance creates difficulties for partitioning their relative contributions to aphid defence. Here we identified isolates of H. defensa that were nearly identical except for APSE type. When holding H. defensa genotype constant, protection levels corresponded to APSE virulence module type. Results further indicated that APSEs move repeatedly within some H. defensa clades providing a mechanism for rapid evolution in anti-parasitoid defences. Strain variation in H. defensa also correlates with the presence of a second symbiont Fukatsuia symbiotica. Predictions that nutritional interactions structured this coinfection were not supported by comparative genomics, but bacteriocin-containing plasmids unique to co-infecting strains may contribute to their common pairing. In conclusion, strain diversity, and joint capacities for horizontal transfer of MGEs and symbionts, are emergent players in the rapid evolution of arthropods.     

Vitamin A inhibition of polyoma virus replication

Vitamin A (retinoic acid) inhibited polyoma virus replication in confluent mouse embryo cells. A significant, dose dependent inhibition was observed when cell monolayers were pretreated with concentrations of vitamin A (10(-8) to 10(-6) M) thought to approximate those found in vivo. This inhibitory effect could be reduced by increasing the input multiplicity of infection. Growth curves of polyoma virus in the presence and absence of vitamin A suggested that vitamin A actually inhibited, and did not simply delay, virus replication. The cell density dependence of this inhibitory effect suggested its association with the prevailing level of cellular DNA synthesis. Vitamin A caused a significant decrease in overall (viral plus cellular) DNA synthesis. Other viruses which do not require induction of host cell DNA synthesis for their replication in confluent, non-dividing cells were not inhibited by vitamin A. These results are consistent with the known inhibitory effects of vitamin A on papovavirus infection in vivo and suggest a mechanism of vitamin A action at the level of the infected cell.     

The adaptation and resistance of Clostridium aminophilum F to the butyrivibriocin-like substance of Butyrivibrio fibrisolvens JL5 and monensin

A collection of 45 epidemiologically unrelated Streptococcus agalactiae strains (group B Streptococcus, GBS), belonging to different serotypes, isolated from pregnant women in China and Russia was studied. Strains were characterized by pulsed-field gel electrophoresis (PFGE) employing hybridization with nine genes potentially involved in virulence. Molecular sizes of GBS genomes varied from 2030 to 2290 kb. Location of the genes under study bac, bca, glnA, scpB, cyl, hylB, lmb, scaA and cfb on the GBS genomes was found to be conserved irrelevant to the serotype. Potential virulence genes scpB, hylB, lmb were located on a 91-kb SmaI fragment that is equal to 4.5% of total genome. Ribotyping of the strains under study revealed three different HindIII, nine EcoRI and 12 PvuII ribotypes among 45 strains. A strong correlation between the PvuII ribotype and the presence of the bac gene was observed, with 21 of 22 bac-positive strains belonging to the same PvuII ribotype P1. PFGE patterns of bac-positive strains were also similar. The possibility of close genetic relatedness of all bac-positive strains is discussed.     

Modelling changes in VOC emission in response to climate change in the continental United States

The alteration of climate is driven not only by anthropogenic activities, but also by biosphere processes that change in conjunction with climate. Emission of volatile organic compounds (VOCs) from vegetation may be particularly sensitive to changes in climate and may play an important role in climate forcing through their influence on the atmospheric oxidative balance, greenhouse gas concentration, and the formation of aerosols. Using the VEMAP vegetation database and associated vegetation responses to climate change, this study examined the independent and combined effects of simulated changes in temperature, CO₂ concentration, and vegetation distribution on annual emissions of isoprene, monoterpenes, and other reactive VOCs (ORVOCs) from potential vegetation of the continental United States. Temperature effects were modelled according to the direct influence of temperature on enzymatic isoprene production and the vapour pressure of monoterpenes and ORVOCs. The effect of elevated CO₂ concentration was modelled according to increases in foliar biomass per unit of emitting surface area. The effects of vegetation distribution reflects simulated changes in species spatial distribution and areal coverage by 21 different vegetation classes. Simulated climate warming associated with a doubled atmospheric CO₂ concentration enhanced total modelled VOC emission by 81.8% (isoprene + 82.1%, monoterpenes + 81.6%, ORVOC + 81.1%), whereas a simulated doubled CO₂ alone enhanced total modelled VOC emission by only + 11.8% (isoprene + 13.7%, monoterpenes + 4.1%, ORVOC + 11.7%). A simulated redistribution of vegetation in response to altered temperatures and precipitation patterns caused total modelled VOC emission to decline by 10.4% (isoprene – 11.7%, monoterpenes – 18.6%, ORVOC 0.0%) driven by a decline in area covered by vegetation classes emitting VOCs at high rates. Thus, the positive effect of leaf-level adjustments to elevated CO₂ (i.e. increases in foliar biomass) is balanced by the negative effect of ecosystem-level adjustments to climate (i.e. decreases in areal coverage of species emitting VOC at high rates).     

The multicomponent antirestriction system of phage P1 is linked to capsid morphogenesis

Bacterial Type I restriction‐modification (R‐M) systems present a major barrier to foreign DNA entering the bacterial cell. The temperate phage P1 packages several proteins into the virion that protect the phage DNA from host restriction. Isogenic P1 deletion mutants were used to reconstitute the previously described restriction phenotypes associated with darA and darB. While P1ΔdarA and P1ΔdarB produced the expected phenotypes, deletions of adjacent genes hdf and ddrA also produced darA‐like phenotypes and deletion of ulx produced a darB‐like phenotype, implicating several new proteins of previously unknown function in the P1 dar antirestriction system. Interestingly, disruption of ddrB decreased P1's sensitivity to EcoB and EcoK restriction. Proteomic analysis of purified virions suggests that packaging of antirestriction components into P1 virions follows a distinct pathway that begins with the incorporation of DarA and Hdf and concludes with DarB and Ulx. Electron microscopy analysis showed that hdf and darA mutants also produce abnormally high proportions of virions with aberrant small heads, which suggests Hdf and DarA play a role in capsid morphogenesis. The P1 antirestriction system is more complex than previously realized and is comprised of multiple proteins including DdrA, DdrB, Hdf, and Ulx in addition to DarA and DarB.     

Understanding the Morphology of PTB7:PCBM Blends in Organic Photovoltaics

The structure–property relationships of PTB7‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM)‐based organic photovoltaics are investigated. The morphology is investigated in an active layer setting where a multi‐length‐scale morphology is observed using a solvent additive‐assisted film processing. This multi‐length‐scale structure consists of a phase separated morphology with a characteristic length scale of ≈30 nm, which is critical for producing large currents in devices; a second length scale of ≈130 nm, arises from face‐on PTB7 crystalline aggregates. This latter morphological feature is also observed in films prepared without the use of an additive. By observing the structure formation in situ during solvent evaporation for blade coated thin films, the additive is found to promote the formation of ordered domains of the PTB7 at an earlier stage during the solvent evaporation, which is critical in the development of the final morphology. In studies on PTB7/PCBM bilayers, PCBM is found to diffuse into the PTB7 layer. However, the performance of devices prepared in this manner is low. This diffusion leads to a swelling of the PTB7 and a reduction in the crystallinity of the PTB7, reflecting the strong miscibility of PCBM with PTB7. The morphology resulting from the interdiffusion is single‐length‐scale with slightly large phase separation. This leads to devices with poor performance.     

Synthesis and characterization of 123I-CMICE-013: A potential SPECT myocardial perfusion imaging agent

Coronary artery disease (CAD) is a major cause of death in Canada and the United States. Single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is a useful diagnostic test in the management of patients with CAD. The widely used SPECT MPI agents, ^99mTc sestamibi and ^99mTc tetrofosmin, exhibit less than ideal pharmacokinetic properties with decreasing uptake with higher flows. ¹²³I has a similar energy as ^99mTc, an ideal half life, and is readily available from cyclotrons. The objective of this study was to develop an ¹²³I labeled MPI agent based on rotenone, a mitochondrial complex I inhibitor, as an alternative to currently available SPECT MPI agents. Methods: ¹²³I-CMICE-013 was synthesized by radiolabeling rotenone with ¹²³I in trifluoroacetic acid (TFA) with iodogen as the oxidizing agent at 60 °C for 45 min, followed by RP-HPLC purification. The product was formulated in 5% EtOH in 10 mM NaOAc pH 6.5. The inactive analog ¹²⁷I-CMICE-013 was isolated and characterized by NMR and mass spectrometry, and the structure determined. Micro-SPECT imaging studies were carried out in normal and infarcted rats. Biodistribution studies were performed in normal rats at 2 h (n = 6) and 24 h (n = 8) post injection (p.i.). Results: ¹²³I-CMICE-013 was isolated with >95% radiochemical purity and high specific activity (14.8–111 GBq/μmol; 400–3000 mCi/μmol). Structural analysis showed that rotenone was iodinated at 7′-position, with removal of the 6′,7′-double bond, and addition of a hydroxy group at 6′-position. MicroSPECT images in normal rats demonstrated homogeneous and sustained myocardial uptake with minimal interference from lung and liver. Absent myocardial perfusion was clearly identified in rats with permanent left coronary artery ligation and ischemia-reperfusion injury. In vivo biodistribution studies in normal rats at 2 h p.i. showed significant myocardial uptake (2.01 ± 0.48%ID/g) and high heart to liver (2.98 ± 0.93), heart to lung (4.11 ± 1.04) and heart to blood (8.37 ± 3.97) ratios. At 24 h p.i., the majority of ¹²³I-CMICE-013 was cleared from tissues, and a significant amount of tracer was found in the thyroid, indicating in vivo deiodination of the tracer. Conclusion: ¹²³I-CMICE-013 is a promising new radiotracer for SPECT MPI with high myocardial uptake, very good target to background ratios and favorable biodistribution characteristics.