A new potential energy surface for ozone is developed. It is based on high level ab initio data and includes an accurate description of the barrier region. Full quantum reactive scattering calculations using a coupled channel approach and hyperspherical coordinates are performed on this surface for various isotopic compositions of ozone. Collision lifetimes are obtained over a wide energy range, which gives the spectrum of rovibrational metastable states ͑scattering resonances͒. This spectrum is discovered to be very nonstatistical. The spectrum of resonances is dense below the isotopic zero-point-energy threshold and sparse above it. This feature is explained by the opening of additional dissociation channels at higher energies. This behavior is a general quantum mechanical effect that should occur in other triatomic molecules.

Almost any warm-blooded creature can be an intermediate host for Toxoplasma gondii. However, sexual reproduction of T. gondii occurs only in felids, wherein fertilisation of haploid macrogametes by haploid microgametes, results in diploid zygotes, around which a protective wall develops, forming unsporulated oocysts. Unsporulated oocysts are shed in the faeces of cats and meiosis gives rise to haploid sporozoites within the oocysts. These, now infectious, sporulated oocysts contaminate the environment as a source of infection for people and their livestock. RNA-Seq analysis of cat enteric stages of T. gondii uncovered genes expressed uniquely in microgametes and macrogametes. A CRISPR/Cas9 strategy was used to create a T. gondii strain that exhibits defective fertilisation, decreased fecundity and generates oocysts that fail to produce sporozoites. Inoculation of cats with this engineered parasite strain totally prevented oocyst excretion following infection with wild-type T. gondii, demonstrating that this mutant is an attenuated, live, transmission-blocking vaccine.

BackgroundThe protozoan Eimeria tenella is a common parasite of chickens, causing avian coccidiosis, a disease of on-going concern to agricultural industries. The high prevalence of E. tenella can be attributed to the resilient oocyst stage, which is transmitted between hosts in the environment. As in related Coccidia, development of the eimerian oocyst appears to be dependent on completion of the parasite’s sexual cycle. RNA Seq transcriptome profiling offers insights into the mechanisms governing the biology of E. tenella sexual stages (gametocytes) and the potential to identify targets for blocking parasite transmission.ResultsComparisons between the sequenced transcriptomes of E. tenella gametocytes and two asexual developmental stages, merozoites and sporozoites, revealed upregulated gametocyte transcription of 863 genes. Many of these genes code for proteins involved in coccidian sexual biology, such as oocyst wall biosynthesis and fertilisation, and some of these were characterised in more depth. Thus, macrogametocyte-specific expression and localisation was confirmed for two proteins destined for incorporation into the oocyst wall, as well as for a subtilisin protease and an oxidoreductase. Homologues of an oocyst wall protein and oxidoreductase were found in the related coccidian, Toxoplasma gondii, and shown to be macrogametocyte-specific. In addition, a microgametocyte gamete fusion protein, EtHAP2, was discovered.ConclusionsThe need for novel vaccine candidates capable of controlling coccidiosis is rising and this panel of gametocyte targets represents an invaluable resource for development of future strategies to interrupt parasite transmission, not just in Eimeria but in other Coccidia, including Toxoplasma, where transmission blocking is a relatively unexplored strategy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1298-6) contains supplementary material, which is available to authorized users.

BackgroundThe apicomplexan parasite Toxoplasma gondii is cosmopolitan in nature, largely as a result of its highly flexible life cycle. Felids are its only definitive hosts and a wide range of mammals and birds serve as intermediate hosts. The latent bradyzoite stage is orally infectious in all warm-blooded vertebrates and establishes chronic, transmissible infections. When bradyzoites are ingested by felids, they transform into merozoites in enterocytes and expand asexually as part of their coccidian life cycle. In all other intermediate hosts, however, bradyzoites differentiate exclusively to tachyzoites, and disseminate extraintestinally to many cell types. Both merozoites and tachyzoites undergo rapid asexual population expansion, yet possess different effector fates with respect to the cells and tissues they develop in and the subsequent stages they differentiate into.ResultsTo determine whether merozoites utilize distinct suites of genes to attach, invade, and replicate within feline enterocytes, we performed comparative transcriptional profiling on purified tachyzoites and merozoites. We used high-throughput RNA-Seq to compare the merozoite and tachyzoite transcriptomes. 8323 genes were annotated with sequence reads across the two asexually replicating stages of the parasite life cycle. Metabolism was similar between the two replicating stages. However, significant stage-specific expression differences were measured, with 312 transcripts exclusive to merozoites versus 453 exclusive to tachyzoites. Genes coding for 177 predicted secreted proteins and 64 membrane- associated proteins were annotated as merozoite-specific. The vast majority of known dense-granule (GRA), microneme (MIC), and rhoptry (ROP) genes were not expressed in merozoites. In contrast, a large set of surface proteins (SRS) was expressed exclusively in merozoites.ConclusionsThe distinct expression profiles of merozoites and tachyzoites reveal significant additional complexity within the T. gondii life cycle, demonstrating that merozoites are distinct asexual dividing stages which are uniquely adapted to their niche and biological purpose.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1225-x) contains supplementary material, which is available to authorized users.

Articles you may be interested inOn the energy dependence of the steric effect in atom-molecule reactive scattering. I. A quasiclassical approach Atom-molecule reactive scattering and symmetrized cross section for the system containing identical nucleiWe describe in detail a new method for solving the coupled linear differential equations which appear in the theoretical statement of many types of scattering phenomena. Combining the speed advantage of propagation methods with the inherent stability of R matrix methods, this method is fast and is unaffected by exponential growth of closed channels. We describe the propagation of the R matrix in terms of a collinear reactive scattering problem, and provide numerical results for several systems, clearly demonstrating the speed, stability, and accuracy of this method. 4272

A new hybrid numerical technique which utilizes both the DVR (Discrete Variable Representation) and FBR (Finite Basis Representation) to solve for the full 5D surface functions in the three-atom problem in hyperspherical coordinates for nonzero total angular momentum (J≠0) is reported. This method accurately treats the Eckart singularities in the kinetic energy operator which occur at both the north pole and equator of the 2D hypersphere in body-frame coordinates. The effects of the Eckart singularities on the surface function energies for HD2 are investigated and it is shown that an accurate treatment of these singularities is crucial in order to obtain the correct results. An improper treatment of the Eckart singularities could be a source for some of the discrepancies between recent experimental results and theory for the reaction H+D2→HD+D.

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A clear explanation for an anomalous isotope effect in ozone formation is given in terms of the energy transfer mechanism, where the metastable states of ozone are formed first, and then stabilized by collisions with other atoms. Unusual nonstatistical properties of metastable states spectra discovered earlier [J. Chem. Phys. 118, 6298 (2003)] are incorporated into the kinetics model, where different metastable states are treated as different species, and the stabilization step is treated approximately. The population of the ozone metastable states builds up and decays through three possible O2+O channels. When different isotopes of oxygen are involved the three channels become open at different energies because of the differences in the quantum zero-point-energies (ΔZPE) of the different O2 molecules. The spectrum of metastable states is anomalously dense below the ΔZPE threshold and these states are accessible only from the lower entrance channel. Also, these low-lying metastable states are stabilized very efficiently (by collisions with third body) because they are energetically close to the bound O3 states. Such processes significantly enhance the formation rates of ozone isotopologues through the lower channels over the formation rates through the upper channels. Numerical results obtained for J=0 give isotope effects in the right direction and of the right order of magnitude. Consideration of J>0 should improve the comparison with experiment.