Mapping of susceptibility to Marek's disease within the major histocompatibility (B) complex by refined typing of White Leghorn chickens

The major histocompatibility (B) complex of a distinct commercial pure White Leghorn chicken line was characterized using serological, biochemical and restriction fragment length polymorphism (RFLP) typing. Line B chickens displayed a high recombination frequency within the B complex. Three recombinant haplo-types were identified. The influence of these haplotypes was determined in relation to the haplotypes B^l9 and B²¹ on their resistance to Marek's disease (MD) in an experimental infection with the virus. Offspring of sires with a recombinant haplotype in combination with B¹⁹ or B²¹, and dams, which were homozygous B¹⁹/B¹⁹ or B²¹/B²¹ were infected. The B type of the offspring had a significant effect upon survival. Animals with B complex types B²¹/B²¹, B¹³⁴/B²¹ and B²³⁴/B²¹ were relatively resistant to MD (24–32% mortality), whereas B¹⁹/B¹⁹ birds were highly susceptible (68% mortality). Animals with a recombinant halpotype B^19r21 (B-G²¹, B-F¹⁹) were equally susceptible to MD as birds with the complete B¹⁹ haplotype. In contrast to earlier publications, resistance was not inherited as a dominant trait. Apparently, B¹⁹ was associated with a dominant susceptibility. The gene(s) associated with the B complex and involved in resistance to MD were localized within the B-F/B-L region. However, the association with a presumably non-coding subregion of B-G could not be excluded.     

Introgressive hybridization of Senecio hercynicus and S. ovatus (Compositae,Senecioneae) along an altitudinal gradient in Harz National Park (Germany)

Introgressive hybridization of Senecio hercynicus and S. ovatus (Compositae, Senecioneae) was studied in a hybrid zone on the southern slopes of Mt Brocken (Harz Mountains, Germany). A total of 415 plants representing 10 stands along an altitudinal gradient were investigated using multivariate statistical analyses of morphological characters and molecular markers (random amplified polymorphic DNA[RAPD]). Both types of traits detected pure S. hercynicus stands on the summit plateau, pure S. ovatus stands at the lowest elevations, and hybrid swarms at intermediate elevations. While morphological and molecular patterns coincided, some individuals in hybrid stands combined morphological patterns typical of S. ovatus with RAPD patterns typical of S. hercynicus, and vice versa. In general, introgression was symmetrical within stands, though one stand combined S. ovatus characters with the glandular hair typical for S. hercynicus, and two stands combined a S. hercynicus typical RAPD genotype with morphological characters shifted towards S. ovatus. Because pure stands of S. hercynicus occurred only on the summit plateau of Mt Brocken, and markers typical for S. ovatus were detectable in stands up to 1040 m a.s.l., future fusion or assimilation of the rare form, S. hercynicus, by the more widespread S. ovatus appears possible at Mt Brocken.     

Negative Effects of Conspecific Floral Density on Fruit Set of Two Neotropical Understory Plants

Plant reproductive success is usually positively related to conspecific floral density, but neutral or negative effects of floral density on reproduction have also been reported. Differences in the relationship between reproduction and floral density largely originate from a trade‐off between increasing attractiveness versus increasing competition for pollinators at high floral densities. Although floral densities strongly vary in the understory of tropical forests, for instance, due to variation in light availability, little is known about the density dependence of reproduction in tropical understory plants. We used path analyses to disentangle direct and indirect effects of canopy openness and floral density on fruit set and analyzed the relationship between pollen load and floral density for two Neotropical understory plants, Heliconia metallica and Besleria melancholica. In both species, fruit set was not directly related to canopy openness, but decreased with increasing floral density. In H. metallica, canopy openness had an indirect negative effect on reproduction mediated by its effects on floral density. Effects of floral density on pollen loads were species‐specific. In B. melancholica, pollen loads linearly decreased with increasing floral density, indicating competition for pollinators at high densities. In H. metallica, pollen loads were reduced at both low and high densities, indicating an interplay of facilitative and competitive effects of floral density on pollen deposition. In contrast to other studies, we found negative density dependence of reproduction in both understory species. Negative effects of floral density on reproduction appear to be related to pollinator‐mediated effects on reproduction rather than to variation in abiotic conditions.     

The reproductive biology of two understory plants in the Atlantic rain forest, Brazil

Outcrossing and sexual reproduction of most flowering plants depends on pollinators. Plant traits likely to be involved in pollinator attraction include flower color, shape, and size. Furthermore, plant or flower density and the temporal flowering pattern may have an effect on reproduction. In this study, we examine the pollination ecology, breeding system, female reproductive output, and germination of two tropical understory species, Stenostephanus lobeliiformis (Acanthaceae) and Besleria melancholica (Gesneriaceae), which differ in these traits. Pollinator observations revealed that the dense flowering S. lobeliiformis with pinkish flowers received a higher diversity of pollinators, but visitor frequency measured as visits per flower per hour was much less (0.1 h^?1) than that to B. melancholica, which has a smaller floral display of dull-colored flowers (1.5 h^?1). Pollination experiments revealed that S. lobeliiformis but not B. melancholica is pollen-limited. In addition, both species are partially self-incompatible and depend on pollinators for outcrossing. Natural fruit set of open-pollinated unmanipulated flowers (control treatment) in both species is 22–26 %. Germination studies indicated inbreeding depression in S. lobeliiformis. We conclude that the pollination ecology of these species is influenced by a broad set of traits and that very different combinations of these traits can be successful in terms of reproduction.     

Genetic structure of coastal and inland populations of the annual halophyte Suaeda maritima (L.) dumort. in Central Europe, inferred from amplified fragment length polymorphism markers

Naturally occurring inland salt habitats are highly threatened due to increasing fragmentation and area reduction, while the surroundings of former potash mining dumps have experienced a massive invasion by halophytes over the last 20 years. We reconstructed colonisation patterns of these purely anthropogenic inland salt sites using molecular markers in the obligate halophyte Suaeda maritima (L.) dumort. (Chenopodiaceae), a typical plant in such areas. In the present study, 120 individual plants from 40 coastal and inland populations in Central Europe were subjected to AFLP analysis with nine primer combinations. A total of 243 AFLP band positions were scored as presence/absence characters. Genetic diversity values were not significantly different in populations from natural and anthropogenic inland salt sites as compared to coastal habitats. Results from principal coordinate analysis, neighbour-joining analysis and analysis of molecular variance ( amova ) all indicated that most of the genetic variation is preserved within populations, while genetic differentiation among populations is comparatively low. We conclude that S. maritima has repeatedly and independently colonised the surroundings of former potash mining dumps in Central Germany. However, the absence of founder effects and the lack of phylogeographic structure prevented us from identifying putative donor populations.     

Whole Cell Formaldehyde Cross-Linking Simplifies Purification of Mitochondrial Nucleoids and Associated Proteins Involved in Mitochondrial Gene Expression

Mitochondrial DNA/protein complexes (nucleoids) appear as discrete entities inside the mitochondrial network when observed by live-cell imaging and immunofluorescence. This somewhat trivial observation in recent years has spurred research towards isolation of these complexes and the identification of nucleoid-associated proteins. Here we show that whole cell formaldehyde crosslinking combined with affinity purification and tandem mass-spectrometry provides a simple and reproducible method to identify potential nucleoid associated proteins. The method avoids spurious mitochondrial isolation and subsequent multifarious nucleoid enrichment protocols and can be implemented to allow for label-free quantification (LFQ) by mass-spectrometry. Using expression of a Flag-tagged Twinkle helicase and appropriate controls we show that this method identifies many previously identified nucleoid associated proteins. Using LFQ to compare HEK293 cells with and without mtDNA, but both expressing Twinkle-FLAG, identifies many proteins that are reduced or absent in the absence of mtDNA. This set not only includes established mtDNA maintenance proteins but also many proteins involved in mitochondrial RNA metabolism and translation and therefore represents what can be considered an mtDNA gene expression proteome. Our data provides a very valuable resource for both basic mitochondrial researchers as well as clinical geneticists working to identify novel disease genes on the basis of exome sequence data.     

Quantification of the Effect of Culturing Temperature on Salt-Induced Heat Resistance of Bacillus Species

Short- and long-term exposure to mild stress conditions can activate stress adaptation mechanisms in pathogens, resulting in a protective effect toward otherwise lethal stresses. The mesophilic strains Bacillus cereus ATCC 14579 and ATCC 10987 and the psychrotolerant strain B. weihenstephanensis KBAB4 were cultured at 12°C and 30°C until the exponential growth phase (i) in the absence of salt, (ii) in the presence of salt, and (iii) with salt shock after they reached the exponential growth phase and subsequently heat inactivated. Both the first-order model and the Weibull model were fitted to the inactivation kinetics, and statistical indices were calculated to select for each condition the most appropriate model to describe the inactivation data. The third-decimal reduction times (which reflected the times needed to reduce the initial number of microorganisms by three decimal powers) were determined for quantitative comparison. The heat resistance of both mesophilic strains increased when cells were salt cultured and salt shocked at 30°C, whereas these salt-induced effects were not significant for the psychrotolerant strain. In contrast, only the psychrotolerant strain showed salt-induced heat resistance when cells were cultured at 12°C. Therefore, culturing temperature and strain diversity are important aspects to address when adaptive stress responses are quantified. The activated adaptive stress response had an even larger impact on the number of surviving microorganisms when the stress factor (i.e., salt) was still present during inactivation. These factors should be considered when stress-integrated predictive models are developed that can be used in the food industry to balance and optimize processing conditions of minimally processed foods.Bacillus cereus is a widespread, spore-forming pathogen that can be isolated from a range of different food products (4, 27), including pastry, vegetables and vegetable products, milk and milk products, and ready-to-eat foods. This toxin-producing pathogen can cause diarrhea and emesis (13, 25). The diarrheal syndrome is caused by several enterotoxins which are produced by vegetative cells in the small intestine. The emetic toxin, cereulide, causes emesis and is produced in foods before ingestion. Adequate chilling of foods is important to control the growth and toxin production of enterotoxin-producing (17) and emetic toxin-producing (7, 18) B. cereus strains.During processing and storage of mildly processed foods, bacteria are exposed to one or more preservation stresses, known as hurdles (16). While individual hurdles might not be effective in controlling microbial growth, the right combination of hurdles can be powerful in controlling microbial growth in minimally processed foods. However, the potential of Bacillus to become more resistant to stresses challenges the effectiveness of minimal processing. Several studies have demonstrated that exposure to mild stressing conditions can result in the increased resistance of both mesophilic and psychrotolerant members of the B. cereus group (2, 3, 5, 21, 22). These studies used optimal culturing temperature during mild stress exposure to investigate the adaptive stress responses. However, during processing, distribution, and storage, the temperature of foods may be lower because chilling is commonly used in the minimal processing food chain. Therefore, investigation of the effect of low incubation temperature on the adaptive stress responses of food-borne bacteria is of great relevance and could provide valuable information for quantitative exposure assessment studies.In the study described here, three representatives of the B. cereus group (12), namely, the mesophilic strains B. cereus ATCC 14579 and ATCC 10987 and the psychrotolerant strain Bacillus weihenstephanensis KBAB4, were cultured at 30°C in the absence and presence of mild salt stress, after which their heat resistance was assessed. Moreover, the culturing of cells was also performed at 12°C to determine the effect of a lowered culturing temperature on the adaptive salt stress responses. The third-decimal reduction time estimates were determined to evaluate the effects of the various culturing variables on the heat resistance of the three strains.