Two new antioxidant flavones from the twigs of Eriosema robustum (Fabaceae)

Phytochemical study of the ethanol extract of the twigs of Eriosema robustum, a Cameroonian medicinal plant resulted to the isolation of two new flavones, 2′,3′,5′,5,7-pentahydroxy-3,4′-dimethoxyflavone (1) and 2′,3,5′,5,7-pentahydroxy-4′-methoxyflavone (2), along with five known compounds: 6-prenylpinocembrin (3), 1-O-heptatriacontanoyl glycerol (4), β-sitosterol (5), stigmasterol (6) and 3-O-β-d-glucopyranoside of sitosterol (7). The structure of the isolated compounds were elucidated on the basis of their NMR, UV and MS data, and by comparison with those reported in the literature. The ethanol crude extract, fractions and some isolated compounds (1–4) were evaluated for their radical scavenging capacity using 2,2-diphenyl-1-picryhydrazyl (DPPH). The crude extract, fraction II, the new compounds namely robusflavones A (1) and B (2) exhibited significant antioxidant activity.     

Intracellular and Extracellular Biomineralization Induced by Klebsiella pneumoniae LH1 Isolated from Dolomites

Abstract

The interaction between bacteria and minerals is very complicated and has been intensively studied in the laboratory and the field in the last few decades, but the processes and mechanisms of biomineralization and mineral precipitation are still not fully understood and need to be explored further. In the present work, biomineralization experiments were undertaken using Klebsiella pneumoniae LH1, collected from a natural surface environment in an area of outcrops of Cambrian dolomite, in a culture medium with various Mg/Ca molar ratios (0, 3, 6 and 12). The mineral precipitates obtained were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectrometer (FTIR), laser scanning confocal microscopy (LSCM) and X-ray photoelectron spectroscopy (XPS). Cells were analyzed with a scanning transmission electron microscope (STEM), high resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED). The composition of amino acids in extracellular polymeric substances (EPS) was also determined. In the experiments it was found that the production of ammonia and the presence of carbonate anhydrase promoted the increase of the medium pH and that minerals are nucleated on the EPS, which consist chiefly of amino acids and negatively-charged organic functional groups. With increasing Mg/Ca ratios, the mineral phases changed, including calcite (100%) at Mg/Ca molar ratio of 0, monohydrocalcite (36.05%) + dypingite (63.95%) at Mg/Ca molar ratio of 3, monohydrocalcite (29.72%) + dypingite (15.48%) + nesquehonite (54.80%) at Mg/Ca molar ratio of 6, and monohydrocalcite (14.2%) + dypingite (1.0%) + nesquehonite (84.80%) at Mg/Ca molar ratio of 12. Some intracellular amorphous calcium- and magnesium-rich inclusions were also detected in K. pneumoniae LH1, suggesting intracellular biomineralization accompanying the extracellular mineral precipitation. This study provides further understanding of the biomineralization processes of microorganisms.     

Irreversible prey diapause as an optimal strategy of a physiologically extended Lotka–Volterra model

We propose an optimal control framework to describe intra-seasonal predator–prey interactions, which are characterized by a continuous-time dynamical model comprising predator and prey density, as well as the energy budget of the prey over the length of a season. The model includes a time-dependent decision variable for the prey, representing the portion of the prey population in time that is active, as opposed to diapausing (a state of physiological rest). The predator follows autonomous dynamics and accordingly it remains active during the season. The proposed model is a generalization of the classical Lotka–Volterra predator–prey model towards non-autonomous dynamics that furthermore includes the effect of an energy variable. The model has been inspired by a specific biological system of predatory mites (Acari: Phytoseiidae) and prey mites (so-called fruit-tree red spider mites) (Acari: Tetranychidae) that feed on leaves of apple trees—its parameters have been instantiated based on laboratory and field studies. The goal of the work is to understand the decisions of the prey mites to enter diapause (a state of physiological rest) given the dynamics of the predatory mites: this is achieved by solving an optimization problem hinging on the maximization of the prey population contribution to the next season. The main features of the optimal strategy for the prey are shown to be that (1) once in diapause, the prey does not become active again within the same season and hence diapause is an irreversible process; (2) for the vast majority of parameter space, the portion of prey individuals entering diapause within the season does not decrease in time; (3) with an increased number of predators, the optimal population strategy for the prey is to start diapause earlier and to enter diapause more gradually. This optimal population strategy will be studied for its ESS properties in a sequel to the work presented in this article.     

Berenil Complexation with a Nucleic Acid Triple Helix

Abstract

The interaction of berenii molecule, a minor groove binding drug, with T-A-T triple helix and A-T double helix was studied using circular dichroism spectroscopy and thermal denaturation. The triple helix was made by an oligonucleotide (dA)₁₂?x-(dT)₁₂?x-(dT)₁₂, where x is a hexaethylene glycol chain bridged between the 3′ phosphate of one strand and the 5′ phosphate of the following strand. This oligonucleotide is able to fold back on itself to form a very stable triplex. Circular dichroism spectroscopy demonstrates that berenil can bind to the triple helical structure. Spectral analysis shows that in the same ionic strength the drug bound to a double-stranded structure exhibits a conformation and an environment close to those observed in triple-stranded structure. The influence of the ionic strength on the interaction between the berenil molecule and the 36-mer is clearly demonstrated. We showed that when no NaCl salt is added in the buffer the triplex form of (dA)₁₂?x-(dT)₁2-x-(dT)₁₂ is stabilized by berenil whereas it is destabilized slightly by the dye when NaCl concentration is 1 M.     

Factors Affecting Work Ability in Day and Shift‐Working Nurses

Satisfactory work ability is sustained and promoted by good physical and mental health and by favorable working conditions. This study examined whether favorable and rewarding work‐related factors increased the work ability among European nurses. The study sample was drawn from the Nurses' Early Exit Study and consisted of 7,516 nursing staff from seven European countries working in state‐owned and private hospitals. In all, 10.8% were day, 4.2% were permanent night, 20.9% were shift without night shift, and 64.1% were shift workers with night shifts. Participants were administered a composite questionnaire at baseline (Time 0) and 1 yr later (Time 1). The Work Ability Index (WAI) at Time 1 was used as the outcome measure, while work schedule, sleep, rewards (esteem and career), satisfaction with pay, work involvement and motivation, and satisfaction with working hours at Time 0 were included as potential determinants of work ability. Univariate and multivariate analyses were conducted after adjusting for a number of confounders (i.e., country, age, sex, type of employment, family status, and other job opportunities in the same area). Work schedule was not related to Time 1 changes in WAI. Higher sleep quality and quantity and more favorable psychosocial factors significantly increased work ability levels. Higher sleep quality and quantity did not mediate the effect of work schedule on work ability. No relevant interaction effects on work ability were observed between work schedule and the other factors considered at Time 0. As a whole, sleep and satisfaction with working time were gradually reduced from day work to permanent night work. However, scores on work involvement, motivation, and satisfaction with pay and rewards were the highest in permanent night workers and the lowest in rotating shift workers that included night shifts.     

Microbially Mediated Calcium Carbonate Precipitation: Implications for Interpreting Calcite Precipitation and for Solid-Phase Capture of Inorganic Contaminants

Microbial degradation of urea was investigated as a potential geochemical catalyst for Ca carbonate precipitation and associated solid phase capture of common groundwater contaminants (Sr, UO₂, Cu) in laboratory batch experiments. Bacterial degradation of urea increased pH and promoted Ca carbonate precipitation in both bacterial control and contaminant treatments. Associated solid phase capture of Sr was highly effective, capturing 95% of the 1 mM Sr added within 24 h. The results for Sr are consistent with solid solution formation rather than discrete Sr carbonate phase precipitation. In contrast, UO₂ capture was not as effective, reaching only 30% of the initial 1 mM UO₂ added, and also reversible, dropping to 7% by 24 h. These results likely reflect differing sites of incorporation of these two elements-Ca lattice sites for Sr versus crystal defect sites for UO₂. Cu sequestration was poor, resulting from toxicity of the metal to the bacteria, which arrested urea degradation and concomitant Ca carbonate precipitation. Scanning electron microscopy (SEM) indicated a variety of morphologies reminiscent of those observed in the marine stromatolite literature. In bacterial control treatments, X-ray diffraction (XRD) analyses indicated only calcite; while in the presence of either Sr or UO₂, both calcite and vaterite, a metastable polymorph of Ca carbonate, were identified. Tapping mode atomic force microscopy (AFM) indicated differences in surface microtopography among abiotic, bacterial control, and bacterial contaminant systems. These results indicate that Ca carbonate precipitation induced by passive biomineralization processes is highly effective and may provide a useful bioremediation strategy for Ca carbonate-rich aquifers where Sr contamination issues exist.     

Characterization in biological traits of entomopathogenic nematodes isolated from North China

In a series of bioassays, thirty-one isolates that were collected from diverse locations in northern China and the laboratory kept isolate Steinernema carpocapsae All, were compared in order to select superior isolates for biological control of Bradysia odoriphaga. Virulence of the isolates against B. odoriphaga was significantly different among nematode isolates. Tolerance of infective juveniles (IJs) to heat, cold, and desiccation differed significantly among and within species. Strains from S. carpocapsae, S. ceratophorum, S. longicaudum, Heterorhabditis indica, and H. bacteriophora were more heat tolerant than strains from S. feltiae, S. hebeiense, S. monticolum, and H. megidis. Heterorhabditis megidis, H. bacteriophora, and S. carpocapsae showed better cold tolerance than the other species. High desiccation tolerance was recorded for S. carpocapsae, S. hebeiense, and S. ceratophorum. The infectivity of IJ of these species against Galleria mellonella larvae was not significantly different between the treated and non-treated IJ after the nematodes had been exposed to 40 °C for 2 h, −5 °C for 8 h or 25% glycerin for 72 h. Nematode survival was significantly affected by exposure time and IJ concentration when exposed to 40 °C or −5 °C. All nematode isolates lost their infectivity against G. mellonella after exposure to −5 °C for 16 h, except for H. megidis LFS10, which had a low infectivity of 3.3%. A hierarchical classification analysis classified the isolates in four main clusters. The fourth cluster, composed of 13 isolates, grouped the isolates that scored well for most traits.     

Alternative phenotypes of male mating behaviour in the two-spotted spider mite

Severe intraspecific competition for mates selects for aggressive individuals but may also lead to the evolution of alternative phenotypes that do not act aggressively, yet manage to acquire matings. The two-spotted spider mite, Tetranychus urticae, shows male mate-guarding behaviour and male–male combat for available females. This may provide opportunity for weaker males to avoid fighting by adopting alternative mating behaviour such as sneaker or satellite tactics as observed in other animals. We investigated male precopulatory behaviour in the two-spotted spider mite by means of video-techniques and found three types of male mating behaviour: territorial, sneaker and opportunistic. Territorial and sneaker males associate with female teleiochrysales and spend much time guarding them. Territorial males are easily disturbed by rival males and engage themselves in fights with them. However, sneaker males are not at all disturbed by rival males, never engage in fights and, strikingly, never face attack by territorial males. Opportunistic males wander around in search of females that are in the teleiochrysalis stage but very close to or at emergence. To quickly classify any given mate-guarding male as territorial or sneaker we developed a method based on the instantaneous response of males to disturbance by a live male mounted on top of a brush. We tested this method against the response of the same males to natural disturbance by two or three other males. Because this method proved to be successful, we used it to collect territorial and sneaker males, and subjected them to morphological analysis to assess whether the various behavioural phenotypes are associated with different morphological characters. However, we found no statistical differences between territorial and sneaker males, concerning the length of the first legs, the stylets, the pedipalps or the body.     

Insights into the carboxyltransferase reaction of pyruvate carboxylase from the structures of bound product and intermediate analogs

Pyruvate carboxylase (PC) is a biotin-dependent enzyme that catalyzes the MgATP- and bicarbonate-dependent carboxylation of pyruvate to oxaloacetate, an important anaplerotic reaction in central metabolism. The carboxyltransferase (CT) domain of PC catalyzes the transfer of a carboxyl group from carboxybiotin to the accepting substrate, pyruvate. It has been hypothesized that the reactive enolpyruvate intermediate is stabilized through a bidentate interaction with the metal ion in the CT domain active site. Whereas bidentate ligands are commonly observed in enzymes catalyzing reactions proceeding through an enolpyruvate intermediate, no bidentate interaction has yet been observed in the CT domain of PC. Here, we report three X-ray crystal structures of the Rhizobium etli PC CT domain with the bound inhibitors oxalate, 3-hydroxypyruvate, and 3-bromopyruvate. Oxalate, a stereoelectronic mimic of the enolpyruvate intermediate, does not interact directly with the metal ion. Instead, oxalate is buried in a pocket formed by several positively charged amino acid residues and the metal ion. Furthermore, both 3-hydroxypyruvate and 3-bromopyruvate, analogs of the reaction product oxaloacetate, bind in an identical manner to oxalate suggesting that the substrate maintains its orientation in the active site throughout catalysis. Together, these structures indicate that the substrates, products and intermediates in the PC-catalyzed reaction are not oriented in the active site as previously assumed. The absence of a bidentate interaction with the active site metal appears to be a unique mechanistic feature among the small group of biotin-dependent enzymes that act on α-keto acid substrates.