Role In Host Recognition Research Articles

Specialist Bombus vestalis and generalist Bombus bohemicus use different odour cues to find their host Bombus terrestris

Cuckoo bumblebees (subgenus Psithyrus) are social parasites in colonies of their host bumblebee species (Bombus). In spring, parasitic females awaken from hibernation and start searching for established host nests. Some Psithyrus species are specialized on one host species, whereas generalists parasitize several species. In previous investigations, nest-marking signals of the bumblebee hosts have been shown to play a role in host recognition and discrimination between host and nonhost. We performed behavioural experiments and comparative chemical analyses with the specialist Bombus (Psithyrus) vestalis and the generalist Bombus (Psithyrus) bohemicus to identify semiochemicals that the females use to recognize the common host, Bombus terrestris. In chemical analyses of footprint samples, we mainly identified nonpolar hydrocarbons and polar wax-type esters. Bioassays with nonpolar and polar fractions obtained by solid phase extraction indicate that specialized parasites use a complex bouquet of compounds for host recognition, whereas generalists need only selected substances common to the signals of all of their hosts. The evolutionary significance of the results is discussed.

Unwrapping the Laccaria genome

Unwrapping the <i>Laccaria</i> genome

Invasive Candida species disease in infants and children: occurrence, risk factors, management, and innate host defense mechanisms

Invasive infections by opportunistic Candida species significantly impact morbidity and mortality. This review provides an update of the incidence, risk factors, and management of invasive candidal disease in infants and children, focusing on very-low-birth-weight neonates, and highlights recent advances in understanding candidal virulence factors and innate anti-Candida species host defense mechanisms. Invasive infections with Candida species are the most common cause of late-onset, blood culture-proven nosocomial sepsis in very-low-birth-weight neonates. Risk factors include colonization, long stay in neonatal intensive care units, and use of broad-spectrum antibiotics, central venous catheters, parenteral nutrition, and mechanical ventilation. These risks are compounded by increasing resistance of Candida species to standard antifungal agents. Recent data suggest that, in addition to the macrophage mannose receptor, beta-glucan receptors, Toll-like receptors, and galectin-3 play an important role in host recognition of Candida species. Reduction of proven risk factors, more aggressive eradication of colonizing fungi by anticandidal agents, and possibly Candida species vaccines may reduce Candida species-associated morbidity and mortality. Accumulating data of molecular mechanisms that underlie innate immune functions against Candida species may provide a basis to prevent and treat candidal infections more efficiently.

The VirB5 protein localizes to the T-pilus tips in Agrobacterium tumefaciens

The Agrobacterium tumefaciens VirB/D4 type IV secretion system (T4SS) mediates the transfer of single-stranded DNA and protein virulence factors into plant cells, and also determines the assembly of the T-pilus, which is believed to play a role in host recognition. The T-pilus is composed of the major component VirB2 and the minor component VirB5. Using immuno-electron microscopy we detected the major component VirB2 along the entire length of detached T-pili, but not on cell-bound T-pili or on the cell surface. In contrast, the minor T-pilus component VirB5 was detected on the tips of cell-bound T-pili as well as on the ends of detached T-pili and on the cell surface. To gain further insights into the role of VirB5 we introduced changes at its C terminus. C-terminal deletions of up to four amino acids and alanine replacements did not abolish T-pilus formation and incorporation of the VirB5 variants at the tip, although they did impact the length of T-pili. Also, these changes differentially affected the ability of the T4SS to transfer DNA into plant and bacterial recipients, suggesting differential effects on host-cell specificity. The data presented here suggest that VirB5 localizes at the T-pilus tip, and provide novel insights into its role during the type IV secretion process.

Response of Pityophthorus puberulus (Coleoptera: Curculionidae: Scolytinae) to pheromones and terpenes

AbstractIn field studies conducted to improve trapping programs for the white pine cone beetle, Conophthorus coniperda (Schwarz), a twig beetle, Pityophthorus puberulus (LeConte), a common associate of eastern white pine, Pinus strobus L. (Pinaceae), in seed orchards, was also captured. In these experiments, P. puberulus was attracted to traps containing the sex pheromone pityol with or without the monoterpenes (−)-α-pinene and (−)-β-pinene, but attraction to traps was inhibited when S-(−)-limonene was present. We speculate that limonene may play an important role in host recognition and suitability, by indicating a resource suitable for C. coniperda but unsuitable for P. puberulus.

Chemical composition of leaf volatiles in Macaranga species (Euphorbiaceae) and their potential role as olfactory cues in host-localization of foundress queens of specific ant partners

Host-plant finding by foundress queens is an important step in the establishment of ant–plant symbioses and olfactory cues may play a crucial role in the Macaranga– Crematogaster ant–plant system for attracting foundresses over longer distances. MicroSPE was used to investigate leaf volatiles of 11 myrmecophytic and non-myrmecophytic Macaranga species. Chemical analysis (GC–MS) yielded a total of 114 compounds comprising a great diversity, including aliphatic compounds, aromatics, mono- and sesquiterpenoids. An analysis of the volatile data using the CNESS distances of the chemical profiles, followed by visualization of the data with non-metric multidimensional scaling (NMDS) showed that even closely related species sharing the same ant partners have clearly different scent patterns. Comparison of spectra of volatile compounds between obligate myrmecophytic Macaranga species and myrmecophilous species that are only facultatively associated with unspecific arboreal ants did not reveal general differences. Choice experiments conducted with foundresses revealed that the ants have the capacity to distinguish between different host species. However, the behavior of the foundresses following surface contact with saplings indicates that other cues, like surface structure, may play a more important role in host-recognition over short distances than volatile compounds. We discuss alternative hypotheses for the possible role of leaf volatiles in the examined Macaranga species as chemical defense against herbivores.

Structural studies on adenoviruses.

The adenovirus genome encodes more than 40 proteins, of which 11 combine with the viral DNA to form an icosahedral capsid of approximately 150 MDa molecular weight and approximately 900 A in diameter. This chapter reviews the information that structural biology techniques have provided about the adenovirus proteins and capsid. The structures of two capsid proteins (hexon and fiber) and two non-structural polypeptides (DNA-binding protein and protease) have been solved by X-ray crystallography. Fiber and its knob have been the focus of the latest structural studies, due to their role in host recognition and consequently in virus targeting for human gene therapy. The current model for the large capsid comes from a combination of electron microscopy and crystallography. The resultant images have revealed a surprising similarity between adenovirus and a bacterial virus, which suggests their common evolutionary origin.

Chemical signals mediating interactions betweenGaleruca tanaceti L. (Coleoptera, Chrysomelidae) and its egg parasitoidOomyzus galerucivorus (Hedqvits) (Hymenoptera, Eulophidae)

Chemical signals mediating interactions betweenGaleruca tanaceti and its egg parasitoidOomyzus galerucivorus (Hymenoptera, Eulophidae) were studied. Neither odor of gravid females ofG. tanaceti nor volatiles of their feces were attractive to the parasitoid. However, the presence of the beetles’ feces on a substrate arrested the parasitoid and elicited frequent antennal drumming. Thus, feces may contain a kairomone important for host finding. Odors of damaged and undamaged host plants had no effect on the parasitoids.O. galerucivorus did not detect its host eggs at close range but encountered them by chance. Neither the structure nor the dark color of the egg surface play a key role in host recognition, but chemicals of the extrachorion which could be isolated by dichloromethane. Fractionation of the dichloromethane extract by TLC revealed a single active fraction which induced host recognition behavior. Since the eggs ofG. tanaceti contain anthraquinones and anthrones which are active as feeding deterrents against predators, we hypothesized that reproductive success ofO. galerucivorus is due to sequestration of these protective compounds. However, GC-MS analyses revealed that there was no transfer of them from the host egg into the adult parasitoid.

Expression of the potato leafroll virus ORF0 induces viral-disease-like symptoms in transgenic potato plants.

The role of the open reading frame 0 (ORF0) of luteoviruses in the viral infection cycle has not been resolved, although the translation product (p28) of this ORF has been suggested to play a role in host recognition. To investigate the function of the potato leafroll luteovirus (PLRV) p28 protein, transgenic potato plants were produced containing the ORF0. In the lines in which the ORF0 transcripts could be detected by Northern (RNA) analysis, the plants displayed an altered phenotype resembling virus-infected plants. A positive correlation was observed between levels of accumulation of the transgenic transcripts and severity of the phenotypic aberrations observed. In contrast, potato plants transformed with a modified, untranslatable ORF0 sequence were phenotypically indistinguishable from wild-type control plants. These results suggest that the p28 protein is involved in viral symptom expression. Southern blot analysis showed that the transgenic plants that accumulated low levels of ORF0 transcripts detectable only by reverse transcription-polymerase chain reaction, contained methylated ORF0 DNA sequences, indicating down-regulation of the transgene provoked by the putatively unfavorable effects p28 causes in the plant cell.

Interferon treatment of murine meth‐a sarcoma cells: Effects on the malignant phenotype and expression of tumor‐specific and H‐2 antigens

A virus-free methycholanthrene-induced sarcoma (Meth-A) in BALB/c mice was grown in culture and treated with purified mouse interferon (alpha and beta mixture) prior to testing for oncogenicity in the host animal. Use of interferon in vitro caused growth inhibition, but not cytotoxic effects; such effects were fully reversible upon interferon removal from the system. There was a significant decrease in tumor incidence in mice challenged with interferon-treated cells, but this could be overcome by sufficiently increasing the number of cells in the inoculating dose. By transplanting these BALB/c sarcoma cells into Sprague-Dawley nude mice, the effects of interferon could be negated. Since these mice have an unaltered activity of NK cells, the results suggest that NK cells do not play a major role in rejection of the Meth-A tumor, but that the reduction in tumor incidence is dependent on the presence of functional T cells. Interferon caused a detectable reduction in the expression of the tumor-specific transplantation antigen (TSTA) associated with Meth-A cells, but increased the expression of H-2 antigens. It has recently been shown that H-2 antigens play a role in host recognition of the TSTA of methylcholanthrene-induced sarcomas. It is suggested that the increased expression of H-2 antigens on interferon-treated Meth-A cells could lead to an increased frequency of recognition by T-cells.