Das Geheimnis des roten Herbstlaubes

The secret of the fall colour red The autumnal coloration of trees and shrubs in temperate climate regions is a well‐known spectacle of nature. Crucial for the yellow colour of leaves is the degradation of chlorophylls which cover the yellow colour of carotenoids. Chlorophyll degradation is a prerequisite for protein degradation and remobilization of precious nitrogen in the amino acids of the chloroplast proteins. In some species leaves turn red in autumn by accumulation of anthocyanins. Anthocyanins can reduce photo‐oxidative stress by acting as a sunscreen shielding against the harmful effects of excess light. Furthermore, anthocyanins prevent the landing of insects – in particular aphides.     

Decoration of Outer Membrane Vesicles with Multiple Antigens by Using an Autotransporter Approach

Outer membrane vesicles (OMVs) are spherical nanoparticles that naturally shed from Gram-negative bacteria. They are rich in immunostimulatory proteins and lipopolysaccharide but do not replicate, which increases their safety profile and renders them attractive vaccine vectors. By packaging foreign polypeptides in OMVs, specific immune responses can be raised toward heterologous antigens in the context of an intrinsic adjuvant. Antigens exposed at the vesicle surface have been suggested to elicit protection superior to that from antigens concealed inside OMVs, but hitherto robust methods for targeting heterologous proteins to the OMV surface have been lacking. We have exploited our previously developed hemoglobin protease (Hbp) autotransporter platform for display of heterologous polypeptides at the OMV surface. One, two, or three of the Mycobacterium tuberculosis antigens ESAT6, Ag85B, and Rv2660c were targeted to the surface of Escherichia coli OMVs upon fusion to Hbp. Furthermore, a hypervesiculating ΔtolR ΔtolA derivative of attenuated Salmonella enterica serovar Typhimurium SL3261 was generated, enabling efficient release and purification of OMVs decorated with multiple heterologous antigens, exemplified by the M. tuberculosis antigens and epitopes from Chlamydia trachomatis major outer membrane protein (MOMP). Also, we showed that delivery of Salmonella OMVs displaying Ag85B to antigen-presenting cells in vitro results in processing and presentation of an epitope that is functionally recognized by Ag85B-specific T cell hybridomas. In conclusion, the Hbp platform mediates efficient display of (multiple) heterologous antigens, individually or combined within one molecule, at the surface of OMVs. Detection of antigen-specific immune responses upon vesicle-mediated delivery demonstrated the potential of our system for vaccine development.     

Variation in human mate choice: simultaneously investigating heritability, parental influence, sexual imprinting, and assortative mating

Human mate choice is central to individuals' lives and to the evolution of the species, but the basis of variation in mate choice is not well understood. Here we looked at a large community-based sample of twins and their partners and parents ([Formula: see text] individuals) to test for genetic and family environmental influences on mate choice, while controlling for and not controlling for the effects of assortative mating. Key traits were analyzed, including height, body mass index, age, education, income, personality, social attitudes, and religiosity. This revealed near-zero genetic influences on male and female mate choice over all traits and no significant genetic influences on mate choice for any specific trait. A significant family environmental influence was found for the age and income of females' mate choices, possibly reflecting parental influence over mating decisions. We also tested for evidence of sexual imprinting, where individuals acquire mate-choice criteria during development by using their opposite-sex parent as the template of a desirable mate; there was no such effect for any trait. The main discernible pattern of mate choice was assortative mating; we found that partner similarity was due to initial choice rather than convergence and also at least in part to phenotypic matching.     

Assessing the efficacy of vesicle fusion with planar membrane arrays using a mitochondrial porin as reporter

Reconstitution of functionally active membrane protein into artificially made lipid bilayers is a challenge that must be overcome to create a membrane-based biomimetic sensor and separation device. In this study we address the efficacy of proteoliposome fusion with planar membrane arrays. We establish a protein incorporation efficacy assay using the major non-specific porin of Fusobacterium nucleatum (FomA) as reporter. We use electrical conductance measurements and fluorescence microscopy to characterize proteoliposome fusion with an array of planar membranes. We show that protein reconstitution in biomimetic membrane arrays may be quantified using the developed FomA assay. Specifically, we show that FomA vesicles are inherently fusigenic. Optimal FomA incorporation is obtained with a proteoliposome lipid-to-protein molar ratio (LPR) = 50 more than 10⁵ FomA proteins could be incorporated in a bilayer array with a total membrane area of 2 mm² within 20 min. This novel assay for quantifying protein delivery into lipid bilayers may be a useful tool in developing biomimetic membrane applications.     

YALI0E32769g (DGA1) and YALI0E16797g (LRO1) encode major triacylglycerol synthases of the oleaginous yeast Yarrowia lipolytica

The oleaginous yeast Yarrowia lipolytica has an outstanding capacity to produce and store triacylglycerols resembling adipocytes of higher eukaryotes. Here, the identification of two genes YALI0E32769g (DGA1) and YALI0E16797g (LRO1) encoding major triacylglycerol synthases of Yarrowia lipolytica is reported. Heterologous expression of either DGA1 or LRO1 in a mutant of the budding yeast Saccharomyces cerevisiae defective in triacylglycerol synthesis restores the formation of this neutral lipid. Whereas Dga1p requires acyl-CoA as a substrate for acylation of diacylglycerol, Lro1p is an acyl-CoA independent triacylglycerol synthase using phospholipids as acyl-donor. Growth of Yarrowia lipolytica strains deleted of DGA1 and/or LRO1 on glucose containing medium significantly decreases triacylglycerol accumulation. Most interestingly, when oleic acid serves as the carbon source the ratio of triacylglycerol accumulation in mutants to wild-type is significantly increased in strains defective in DGA1 but not in lro1Δ. In vitro experiments revealed that under these conditions an additional acyl-CoA dependent triacylglycerol synthase contributes to triacylglycerol synthesis in the respective mutants. Taken together, evidence is provided that Yarrowia lipolytica contains at least four triacylglycerol synthases, namely Lro1p, Dga1p and two additional triacylglycerol synthases whereof one is acyl-CoA dependent and specifically induced upon growth on oleic acid.     

SagS contributes to the motile-sessile switch and acts in concert with BfiSR to enable Pseudomonas aeruginosa biofilm formation

The interaction of Pseudomonas aeruginosa with surfaces has been described as a two-stage process requiring distinct signaling events and the reciprocal modulation of small RNAs (sRNAs). However, little is known regarding the relationship between sRNA-modulating pathways active under planktonic or surface-associated growth conditions. Here, we demonstrate that SagS (PA2824), the cognate sensor of HptB, links sRNA-modulating activities via the Gac/HptB/Rsm system postattachment to the signal transduction network BfiSR, previously demonstrated to be required for the development of P. aeruginosa. Consistent with the role of SagS in the GacA-dependent HtpB signaling pathway, inactivation of sagS resulted in hyperattachment, an HptB-dependent increase in rsmYZ, increased Psl polysaccharide production, and increased virulence. Moreover, sagS inactivation rescued attachment but abrogated biofilm formation by the ΔgacA and ΔhptB mutant strains. The ΔsagS strain was impaired in biofilm formation at a stage similar to that of the previously described two-component system BfiSR. Expression of bfiR but not bfiS restored ΔsagS biofilm formation independently of rsmYZ. We demonstrate that SagS interacts directly with BfiS and only indirectly with BfiR, with the direct and specific interaction between these two membrane-bound sensors resulting in the modulation of the phosphorylation state of BfiS in a growth-mode-dependent manner. SagS plays an important role in P. aeruginosa virulence in a manner opposite to that of BfiS. Our findings indicate that SagS acts as a switch by linking the GacA-dependent sensory system under planktonic conditions to the suppression of sRNAs postattachment and to BfiSR, required for the development of P. aeruginosa biofilms, in a sequential and stage-specific manner.     

Floral isolation is the main reproductive barrier among closely related sexually deceptive orchids

Floral isolation is an important component of pollinator-driven speciation. However, up to now, only a few studies have quantified its strength and relative contribution to total reproductive isolation. In this study, we quantified floral isolation among three closely related, sympatric orchid species of the genus Ophrys by directly tracking pollen flow. Ophrys orchids mimic their pollinators' mating signals, and are pollinated by male insects during mating attempts. This pollination system, called sexual deception, is usually highly specific. However, whether pollinator specialization also conveys floral isolation is currently under debate. In this study, we found strong floral isolation: among 46 tracked pollen transfers in two flowering seasons, all occurred within species. Accounting for observation error rate, we estimated a floral isolation index ≥0.98 among each pair of species. Hand pollination experiments suggested that postpollination barriers were effectively absent among our study species. Genetic analysis based on AFLP markers showed a clear species clustering and very few F(1) hybrids in natural populations, providing independent evidence that strong floral isolation prevents significant interspecies gene flow. Our results provide the first direct evidence that floral isolation acts as the main reproductive barrier among closely related plant species with specialized pollination.     

A whole-genome single nucleotide polymorphism-based approach to trace and identify outbreaks linked to a common Salmonella enterica subsp. enterica serovar Montevideo pulsed-field gel electrophoresis type

In this study, we report a whole-genome single nucleotide polymorphism (SNP)-based evolutionary approach to study the epidemiology of a multistate outbreak of Salmonella enterica subsp. enterica serovar Montevideo. This outbreak included 272 cases that occurred in 44 states between July 2009 and April 2010. A case-control study linked the consumption of salami made with contaminated black and red pepper to the outbreak. We sequenced, on the SOLiD System, 47 isolates with XbaI PFGE pattern JIXX01.0011, a common pulsed-field gel electrophoresis (PFGE) pattern associated with isolates from the outbreak. These isolates represented 20 isolates collected from human sources during the period of the outbreak and 27 control isolates collected from human, food, animal, and environmental sources before the outbreak. Based on 253 high-confidence SNPs, we were able to reconstruct a tip-dated molecular clock phylogeny of the isolates and to assign four human isolates to the actual outbreak. We developed an SNP typing assay to rapidly discriminate between outbreak-related cases and non-outbreak-related cases and tested this assay on an extended panel of 112 isolates. These results suggest that only a very small percentage of the human isolates with the outbreak PFGE pattern and obtained during the outbreak period could be attributed to the actual pepper-related outbreak (20%), while the majority (80%) of the putative cases represented background cases. This study demonstrates that next-generation-based SNP typing provides the resolution and accuracy needed for outbreak investigations of food-borne pathogens that cannot be distinguished by currently used subtyping methods.     

HIV-integrase aptamer folds into a parallel quadruplex: a thermodynamic study

Short guanine-rich sequences have a tendency to form quadruplexes that are stabilized by G-quartets with specific cation coordination. Quadruplexes are part of telomeres at the ends of chromosomes and play an important role in the regulation of gene expression. In addition, there is a strong interest in the therapeutic and biotechnological potential of quadruplex oligonucleotides. The HIV-integrase aptamer, d(GGGT)(4), demonstrated unusually favorable van't Hoff thermodynamics, and based on NMR studies the aptamer was proposed to fold into an antiparallel structure. Here we probed an apparent discrepancy between the NMR structure and the quadruplex topology suggested by circular dichroism (CD). Systematic thermodynamic analyses of d(GGGT)(4) and variants containing sequence modifications or missing specific nucleotides are consistent with a parallel quadruplex fold. CD studies carried out over a wide concentration range did not support a possible structural transition upon increasing strand concentration. Taken together, both optical and thermodynamic studies performed here strongly support a parallel fold for the d(GGGT)(4) aptamer.