Bill redness is positively associated with reproduction and survival in male and female zebra finches

Sexual traits can serve as honest indicators of phenotypic quality when they are costly. Brightly coloured yellow to red traits, which are pigmented by carotenoids, are relatively common in birds, and feature in sexual selection. Carotenoids have been linked to immune and antioxidant function, and the trade-off between ornamentation and these physiological functions provides a potential mechanism rendering carotenoid based signals costly. Mutual ornamentation is also common in birds and can be maintained by mutual mate choice for this ornament or by a correlated response in one sex to selection on the other sex. When selection pressures differ between the sexes this can cause intralocus sexual conflict. Sexually antagonistic selection pressures have been demonstrated for few sexual traits, and for carotenoid-dependent traits there is a single example: bill redness was found to be positively associated with survival and reproductive output in male zebra finches, but negatively so in females. We retested these associations in our captive zebra finch population without two possible limitations of this earlier study. Contrary to the earlier findings, we found no evidence for sexually antagonistic selection. In both sexes, individuals with redder bills showed higher survival. This association disappeared among the females with the reddest bills. Furthermore, females with redder bills achieved higher reproductive output. We conclude that bill redness of male and female zebra finches honestly signals phenotypic quality, and discuss the possible causes of the differences between our results and earlier findings.     

Assessment of Heat Resistance of Bacterial Spores from Food Product Isolates by Fluorescence Monitoring of Dipicolinic Acid Release

This study is aimed at the development and application of a convenient and rapid optical assay to monitor the wet-heat resistance of bacterial endospores occurring in food samples. We tested the feasibility of measuring the release of the abundant spore component dipicolinic acid (DPA) as a probe for heat inactivation. Spores were isolated from the laboratory type strain Bacillus subtilis 168 and from two food product isolates, Bacillus subtilis A163 and Bacillus sporothermodurans IC4. Spores from the lab strain appeared much less heat resistant than those from the two food product isolates. The decimal reduction times (D values) for spores from strains 168, A163, and IC4 recovered on Trypticase soy agar were 1.4, 0.7, and 0.3 min at 105°C, 120°C, and 131°C, respectively. The estimated Z values were 6.3°C, 6.1°C, and 9.7°C, respectively. The extent of DPA release from the three spore crops was monitored as a function of incubation time and temperature. DPA concentrations were determined by measuring the emission at 545 nm of the fluorescent terbium-DPA complex in a microtiter plate fluorometer. We defined spore heat resistance as the critical DPA release temperature (T_c), the temperature at which half the DPA content has been released within a fixed incubation time. We found T_c values for spores from Bacillus strains 168, A163, and IC4 of 108°C, 121°C, and 131°C, respectively. On the basis of these observations, we developed a quantitative model that describes the time and temperature dependence of the experimentally determined extent of DPA release and spore inactivation. The model predicts a DPA release rate profile for each inactivated spore. In addition, it uncovers remarkable differences in the values for the temperature dependence parameters for the rate of spore inactivation, DPA release duration, and DPA release delay.     

Construction of a bacterial artificial chromosome (BAC) library of Lycopersicon esculentum cv. Stevens and its application to physically map the Sw-5 locus

The Sw-5 gene is a dominantly inherited resistance gene in tomato and functional against a number of tospovirus species. The gene has been mapped on chromosome 9, tightly linked to RFLP markers CT220 and SCAR421. To analyse the Sw-5 locus, a BAC genomic library was constructed of tomato cv. Stevens, homozygous for the Sw-5 gene. The library comprised 18 816 clones with an average insert size of 100 kb, corresponding to two genome equivalents. The library was screened by PCR using primers designed for the CT220 and SCAR421 sequences, resulting in a 250 kb contig of known orientation on the long arm of chromosome 9. Using degenerate primers based on homologous sequences in the nucleotide binding site of resistance gene sequences, three discrete PCR fragments obtained from this contig were cloned and sequenced. Analysis of these fragments revealed a high similarity with numerous resistance genes or resistance gene like sequences. The present data indicate that at least three different resistance gene candidate (RGC) sequences are present in the vicinity of marker CT220, supporting the view that a resistance gene family may be responsible for the unusually broad resistance to tospoviruses conferred by the Sw-5 locus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Attraction of the specialist parasitoid Cotesia rubecula to Arabidopsis thaliana infested by host or non-host herbivore species

In this study we investigated whether in a two‐choice set‐up the parasitoid Cotesia rubecula (Marshall) (Hymenoptera, Braconidae) distinguishes between volatiles emitted by Arabidopsis thaliana (L.) Heynh. (Brassicaceae) infested with its host, Pieris rapae (L.) (Lepidoptera: Pieridae) and Arabidopsis infested with non‐host herbivores. Four non‐host herbivore species were tested: the caterpillars Plutella xylostella (L.) (Lepidoptera: Plutellidae) and Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), both chewing insects, the spider mite Tetranychus urticae (Koch) (Acari: Tetranychidae), which punctures parenchymal cells, and the aphid Myzus persicae (Sulzer) (Hemiptera: Aphidoidea), which is a phloem‐feeder. Compared with undamaged plants, C. rubecula females were more attracted to Arabidopsis plants infested by P. rapae, P. xylostella, S. exigua, or T. urticae, but not to plants infested by M. persicae. The parasitoids preferred host‐infested plants to spider mite‐ or aphid‐infested plants, but not to plants infested with non‐host caterpillars (P. xylostella or S. exigua). The data show that when Arabidopsis plants are infested with a leaf tissue‐damaging herbivore they emit a volatile blend that attracts C. rubecula females and the wasps only discriminate between a host and non‐host herbivore when the type of damage is different (chewing vs. piercing). When Arabidopsis is infested with a herbivore that hardly damages leaf tissue, C. rubecula females are not attracted. These results may be explained by differences in the amount of damage and in the relative importance of different signal‐transduction pathways induced by different types of herbivores.     

Current topics in signal transduction in bacteria

Among the signal transfer systems in bacteria two types predominate: two-component regulatory systems and quorum sensing systems. Both types of system can mediate signal transfer across the bacterial cell envelope; however, the signalling molecule typically is not taken up into the cells in the former type of system, whereas it usually is in the latter. The Two-component systems include the recently described (eukaryotic) phosphorelay systems; quorum sensing systems can be based upon autoinducers of the N-acylated homoserine lactones, and on autoinducers of a peptidic nature. A single bacterial cell contains many signalling modules that primarily operate in parallel. This may give rise to neural-network behaviour. Recently, however, for both types of basic signal transfer modules, it has been demonstrated that they also can be organised in series (i.e. in a hierarchical order). Besides their hierarchical position in the signal transduction network of the cell, the spatial distribution of individual signalling modules may also be an important factor in their efficiency in signal transfer. Many challenges lie hidden in future work to understand these signal transfer processes in more detail. These are discussed here, with emphasis on the mutual interactions between different signal transfer processes. Successful contributions to this work will require rigorous mathematical modelling of the performance of signal transduction components, and -networks, as well as studies on light-sensing signal transduction systems, because of the unsurpassed time resolution obtainable in those latter systems, the opportunity to apply repeated reproducible stimuli, etc. The increased understanding of bacterial behaviour that already has resulted – and may further result – from these studies, can be used to fine-tune the beneficial activities of bacteria and/or more efficiently inhibit their deleterious ones.     

Identification of a 3.0-kb major recombination hotspot in patients with Sotos syndrome who carry a common 1.9-Mb microdeletion

Sotos syndrome (SoS) is a congenital dysmorphic disorder characterized by overgrowth in childhood, distinctive craniofacial features, and mental retardation. Haploinsufficiency of the NSD1 gene owing to either intragenic mutations or microdeletions is known to be the major cause of SoS. The common approximately 2.2-Mb microdeletion encompasses the whole NSD1 gene and neighboring genes and is flanked by low-copy repeats (LCRs). Here, we report the identification of a 3.0-kb major recombination hotspot within these LCRs, in which we mapped deletion breakpoints in 78.7% (37/47) of patients with SoS who carry the common microdeletion. The deletion size was subsequently refined to 1.9 Mb. Sequencing of breakpoint fragments from all 37 patients revealed junctions between a segment of the proximal LCR (PLCR-B) and the corresponding region of the distal LCR (DLCR-2B). PLCR-B and DLCR-2B are the only directly oriented regions, whereas the remaining regions of the PLCR and DLCR are in inverted orientation. The PLCR, with a size of 394.0 kb, and the DLCR, with a size of of 429.8 kb, showed high overall homology (approximately 98.5%), with an increased sequence similarity (approximately 99.4%) within the 3.0-kb breakpoint cluster. Several recombination-associated motifs were identified in the hotspot and/or its vicinity. Interestingly, a 10-fold average increase of a translin motif, as compared with the normal distribution within the LCRs, was recognized. Furthermore, a heterozygous inversion of the interval between the LCRs was detected in all fathers of the children carrying a deletion in the paternally derived chromosome. The functional significance of these findings remains to be elucidated. Segmental duplications of the primate genome play a major role in chromosomal evolution. Evolutionary study showed that the duplication of the SoS LCRs occurred 23.3-47.6 million years ago, before the divergence of Old World monkeys.     

Di-epoxides of the three isomeric dicyclopenta-fused pyrenes: ultimate mutagenic active agents

To rationalize the high bacterial mutagenic response recently found for the (di-) cyclopenta-fused pyrene congeners, viz. cyclopenta[cd]-(1), dicyclopenta[cd,mn]-(2), dicyclopenta[cd,fg]-(3) and dicyclopenta[cd,jk]pyrene (4), in the presence of a metabolic activation mixture (S9-mix), their (di-)epoxides at the externally fused unsaturated five-membered rings were previously proposed as the ultimate mutagenic active forms. In this study, cyclopenta[cd]pyrene-3,4-epoxide (5) and the novel dicyclopenta[cd,mn]pyrene-1,2,4,5-di-epoxide (6), dicyclopenta[cd,fg]pyrene-5,6,7,8-di-epoxide (7) and dicyclopenta[cd,jk]pyrene-1,2,6,7-di-epoxide (8) were synthesised from 1 to 4, respectively, and subsequently assayed for bacterial mutagenicity in the standard microsomal/histidine reverse mutation assay (Ames-assay with Salmonella typhimurium strain TA98). The di-epoxides 6-8 are present as a mixture of their cis- and trans-stereo-isomers in a close to 1:1 ratio ((1)H NMR spectroscopy and ab initio IGLO/III//RHF/6-31G** calculations). The direct-acting mutagenic activity and the strong cytotoxicity exerted by 5-8 both in the absence or presence of an exogenous metabolic activation system (+/-S9-mix) demonstrate that the ultimate mutagenic active forms are the proposed (di-)epoxides of 1-4.     

Multiparameter Viability Assay for Stress Profiling Applied to the Food Pathogen Listeria monocytogenes F2365

A novel generic approach for stress profiling was applied to Listeria monocytogenes strain F2365. This food-borne pathogen was exposed to gradients of five different stresses of increasing intensity, typically ranging from moderate to lethal conditions. The stress factors included heat, acidic pH, a detergent disinfectant, an oxidant, and hyperosmotic conditions. In addition to CFU counts and lag time, five different molecular viability parameters were measured by fluorescence-based assays, including membrane integrity, membrane potential, esterase activity, redox activity, and intracellular pH stability. The last was measured by our recently invented real-time viability assay. Exposure to all stresses resulted in clear dose-response relationships for all viability parameters with the exception of hyperosmotic conditions. A statistical analysis showed strong correlations for (i) the growth parameters plate counts and lag times, (ii) the enzyme-associated functions redox and esterase activity, and (iii) the membrane-associated pH stability and membrane integrity. Results indicated a pronounced difference in the susceptibilities of the measured parameters depending on the stress factor applied. However, at relatively high stress intensities, all of the viability parameters became affected independent of the stress factor. Applications of the approach presented here include studies on the mechanism of action of unknown compounds with biocidal activity and a comparative analysis of the severities of the impact of stress conditions of interest. It appears that a meaningful evaluation of the impact of mild stress conditions can be obtained only through measurement of multiple viability parameters.     

Glutamate as chemotactic fuel for diffuse glioma cells: Are they glutamate suckers?

Diffuse gliomas comprise a group of primary brain tumors that originate from glial (precursor) cells and present as a variety of malignancy grades which have in common that they grow by diffuse infiltration. This phenotype complicates treatment enormously as it precludes curative surgery and radiotherapy. Furthermore, diffusely infiltrating glioma cells often hide behind a functional blood–brain barrier, hampering delivery of systemically administered therapeutic and diagnostic compounds to the tumor cells. The present review addresses the biological mechanisms that underlie the diffuse infiltrative phenotype, knowledge of which may improve treatment strategies for this disastrous tumor type. The invasive phenotype is specific for glioma: most other brain tumor types, both primary and metastatic, grow as delineated lesions. Differences between the genetic make-up of glioma and that of other tumor types may therefore help to unravel molecular pathways, involved in diffuse infiltrative growth. One such difference concerns mutations in the NADP⁺-dependent isocitrate dehydrogenase (IDH1 and IDH2) genes, which occur in > 80% of cases of low grade glioma and secondary glioblastoma. In this review we present a novel hypothesis which links IDH1 and IDH2 mutations to glutamate metabolism, possibly explaining the specific biological behavior of diffuse glioma.