High‐Voltage Photogeneration Exclusively via Aggregation‐Induced Triplet States in a Heavy‐Atom‐Free Nonplanar Organic Semiconductor

The electron–hole recombination kinetics of organic photovoltaics (OPVs) are known to be sensitive to the relative energies of triplet and charge‐transfer (CT) states. Yet, the role of exciton spin in systems having CT states above 1.7 eV—like those in near‐ultraviolet‐harvesting OPVs—has largely not been investigated. Here, aggregation‐induced room‐temperature intersystem crossing (ISC) to facilitate exciton harvesting in OPVs having CT states as high as 2.3 eV and open‐circuit voltages exceeding 1.6 V is reported. Triplet excimers from energy‐band splitting result in ultrafast CT and charge separation with nonradiative energy losses of <250 meV, suggesting that a 0.1 eV driving force is sufficient for charge separation, with entropic gain via CT state delocalization being the main driver for exciton dissociation and generation of free charges. This finding can inform engineering of next‐generation active materials and films for near‐ultraviolet OPVs with open‐circuit voltages exceeding 2 V. Contrary to general belief, this work reveals that exclusive and efficient ISC need not require heavy‐atom‐containing active materials. Molecular aggregation through thin‐film processing provides an alternative route to accessing 100% triplet states on photoexcitation.     

Surfactin and fengycin contribute to the protection of a Bacillus subtilis strain against grape downy mildew by both direct effect and defence stimulation

Bacillus subtilis GLB191 (hereafter GLB191) is an efficient biological control agent against the biotrophic oomycete Plasmopara viticola, the causal agent of grapevine downy mildew. In this study, we show that GLB191 supernatant is also highly active against downy mildew and that the activity results from both direct effect against the pathogen and stimulation of the plant defences (induction of defence gene expression and callose production). High-performance thin-layer chromatography analysis revealed the presence of the cyclic lipopeptides fengycin and surfactin in the supernatant. Mutants affected in the production of fengycin and/or surfactin were thus obtained and allowed us to show that both surfactin and fengycin contribute to the double activity of GLB191 supernatant against downy mildew. Altogether, this study suggests that GLB191 supernatant could be used as a new biocontrol product against grapevine downy mildew.     

Combination of high-throughput microfluidics and FACS technologies to leverage the numbers game in natural product discovery

High-throughput platforms facilitating screening campaigns of environmental samples are needed to discover new products of natural origin counteracting the spreading of antimicrobial resistances constantly threatening human and agricultural health. We applied a combination of droplet microfluidics and fluorescence-activated cell sorting (FACS)-based technologies to access and assess a microbial environmental sample. The cultivation performance of our microfluidics workflow was evaluated in respect to the utilized cultivation media by Illumina amplicon sequencing of a pool of millions of droplets, respectively. This enabled the rational selection of a growth medium supporting the isolation of microbial diversity from soil (five phyla affiliated to 57 genera) including a member of the acidobacterial subgroup 1 (genus Edaphobacter). In a second phase, the entire diversity covered by 1071 cultures was used for an arrayed bioprospecting campaign, resulting in > 6000 extracts tested against human pathogens and agricultural pests. After redundancy curation by using a combinatorial chemical and genomic fingerprinting approach, we assigned the causative agents present in the extracts. Utilizing UHPLC-QTOF-MS/MS-guided fractionation and microplate-based screening assays in combination with molecular networking the production of bioactive ionophorous macrotetrolides, phospholipids, the cyclic lipopetides massetolides E, F, H and serratamolide A and many derivatives thereof was shown.     

Induced prion protein controls immune-activated retroviruses in the mouse spleen

The prion protein (PrP) is crucially involved in transmissible spongiform encephalopathies (TSE), but neither its exact role in disease nor its physiological function are known. Here we show for mice, using histological, immunochemical and PCR-based methods, that stimulation of innate resistance was followed by appearance of numerous endogenous retroviruses and ensuing PrP up-regulation in germinal centers of the spleen. Subsequently, the activated retroviruses disappeared in a PrP-dependent manner. Our results reveal the regular involvement of endogenous retroviruses in murine immune responses and provide evidence for an essential function of PrP in the control of the retroviral activity. The interaction between PrP and ubiquitous endogenous retroviruses may allow new interpretations of TSE pathophysiology and explain the evolutionary conservation of PrP.     

Computational models evaluating the impact of sieve plates and radial water exchange on phloem pressure gradients

The sugar conducting phloem in angiosperms is a high resistance pathway made up of sieve elements bounded by sieve plates. The high resistance generated by sieve plates may be a trade‐off for promoting quick sealing in the event of injury. However, previous modeling efforts have demonstrated a wide variation in the contribution of sieve plates towards total sieve tube resistance. In the current study, we generated high resolution scanning electron microscope images of sieve plates from balsam poplar and integrated them into a mathematical model using Comsol Multiphysics software. We found that sieve plates contribute upwards of 85% towards total sieve tube resistance. Utilizing the Navier–Stokes equations, we found that oblong pores may create over 50% more resistance in comparison with round pores of the same area. Although radial water flows in phloem sieve tubes have been previously considered, their impact on alleviating pressure gradients has not been fully studied. Our novel simulations find that radial water flow can reduce pressure requirements by half in comparison with modeled sieve tubes with no radial permeability. We discuss the implication that sieve tubes may alleviate pressure requirements to overcome high resistances by regulating their membrane permeability along the entire transport pathway.     

Peripheral and central fatigue after muscle-damaging exercise is muscle length dependent and inversely related

Healthy untrained men performed 10 series of 12 knee eccentric extension repetitions (EE) at 160°/s. The maximal voluntary isometric contraction force of the quadriceps muscle, the maximal rate of electrically induced torque development (RTD) and relaxation (RTR), isokinetic concentric torque at 30°/s, the electrostimulation-induced torque at 20 and 100 Hz frequencies were established before and after EE at shorter and longer muscle lengths. Besides, voluntary activation (VA) index and central activation ratio (CAR) were tested. There was more peripheral fatigue than central after EE. We established more central fatigue as well as low frequency fatigue at a shorter muscle length compared to the longer muscle length. Relative RTD as well as relative RTR, improved after EE and did not depend on the muscle length. Finally, central fatigue is inversely significantly related with the eccentric torque reduction during eccentric exercise and with the changes in muscle torque induced by low frequency stimulation.     

Rhodocytin (aggretin) activates platelets lacking alpha(2)beta(1) integrin, glycoprotein VI, and the ligand-binding domain of glycoprotein Ibalpha

Although alpha(2)beta(1) integrin (glycoprotein Ia/IIa) has been established as a platelet collagen receptor, its role in collagen-induced platelet activation has been controversial. Recently, it has been demonstrated that rhodocytin (also termed aggretin), a snake venom toxin purified from the venom of Calloselasma rhodostoma, induces platelet activation that can be blocked by monoclonal antibodies against alpha(2)beta(1) integrin. This finding suggested that clustering of alpha(2)beta(1) integrin by rhodocytin is sufficient to induce platelet activation and led to the hypothesis that collagen may activate platelets by a similar mechanism. In contrast to these findings, we provided evidence that rhodocytin does not bind to alpha(2)beta(1) integrin. Here we show that the Cre/loxP-mediated loss of beta(1) integrin on mouse platelets has no effect on rhodocytin-induced platelet activation, excluding an essential role of alpha(2)beta(1) integrin in this process. Furthermore, proteolytic cleavage of the 45-kDa N-terminal domain of glycoprotein (GP) Ibalpha either on normal or on beta(1)-null platelets had no significant effect on rhodocytin-induced platelet activation. Moreover, mouse platelets lacking both alpha(2)beta(1) integrin and the activating collagen receptor GPVI responded normally to rhodocytin. Finally, even after additional proteolytic removal of the 45-kDa N-terminal domain of GPIbalpha rhodocytin induced aggregation of these platelets. These results demonstrate that rhodocytin induces platelet activation by mechanisms that are fundamentally different from those induced by collagen.     

Evidence for two distinct epitopes within collagen for activation of murine platelets

It has recently been shown that the monoclonal antibody JAQ1 to murine glycoprotein VI (GPVI) can cause aggregation of mouse platelets upon antibody cross-linking and that collagen-induced platelet aggregation can be inhibited by preincubation of platelets with JAQ1 in the absence of cross-linking (Nieswandt, B., Bergmeier, W., Schulte, V., Rackebrandt, K., Gessner, J. E., and Zirngibl, H. (2000) J. Biol. Chem. 275, 23998-24002). In the present study, we have shown that cross-linking of GPVI by JAQ1 results in tyrosine phosphorylation of the same profile of proteins as that induced by collagen, including the Fc receptor (FcR) gamma-chain, Syk, LAT, SLP-76, and phospholipase C gamma 2. In contrast, platelet aggregation and tyrosine phosphorylation of these proteins were inhibited when mouse platelets were preincubated with JAQ1 in the absence of cross-linking and were subsequently stimulated with a collagen-related peptide (CRP) that is specific for GPVI and low concentrations of collagen. However, at higher concentrations of collagen, but not CRP, aggregation of platelets and tyrosine phosphorylation of the above proteins (except for the adapter LAT) is re-established despite the presence of JAQ1. These observations suggest that a second activatory binding site, which is distinct from the CRP binding site on GPVI on mouse platelets, is occupied in the presence of high concentrations of collagen. Although this could be a second site on GPVI that is activated by a novel motif within the collagen molecule, the absence of LAT phosphorylation in response to collagen in the presence of JAQ1 suggests that this is more likely to be caused by activation of a second receptor that is also coupled to the FcR gamma-chain. The possibility that this response is mediated by a receptor that is not coupled to FcR gamma-chain is excluded on the grounds that aggregation is absent in platelets from FcR gamma-chain-deficient mice.     

Microplate enzyme-coupled assays of mevalonate and phosphomevalonate kinase from Catharanthus roseus suspension cultured cells

A microplate assay for mevalonate and 5-phosphomevalonate kinase activities has been developed using an enzyme-coupled system of pyruvate kinase and lactate dehydrogenase. Mevalonate and 5-phosphomevalonate kinase activities were measured in crude and partially purified enzyme preparations from Catharanthus roseus suspension-cultured plant cells. The assay was validated with respect to protein and substrate concentration. Mevalonate and 5-phosphomevalonate kinase showed Michaelis-Menten kinetics with respect to ATP and their specific substrates; the apparent Km values of mevalonate kinase for ATP and mevalonate were 210 and 65 microM, respectively, and of 5-phosphomevalonate kinase for ATP and 5-phosphomevalonate were 0.41 and 0.4 mM, respectively. Considering mevalonate kinase, the relative standard deviation of enzyme activity within a determination (n = 3) is always less than 2.5% and in between determinations (n = 9) is less than 2%. The method can be used in a continuous assay as well as in a discontinuous assay.