Acclimation Response of Green Microalgae Chlorella Sorokiniana to 2,3′,4,4′,6-Pentachlorobiphenyl

The effect of the toxicant 2,3′,4,4′,6-pentachlorobiphenyl (PCB-119) on the growth, chlorophyll content, and PSII activity of C. sorokiniana cells was investigated. A strong negative effect of the toxicant was observed at PCB concentration of 0.05 μg mL⁻¹, when culture growth ceased, chlorophyll strongly bleached, and cell death occurred. The use of original highly sensitive fluorimeter to measure three types of high-resolution chlorophyll fluorescence kinetics allowed us to detect an initial dramatic decrease in the activity of primary photosynthetic reactions, followed by their almost complete recovery at the end of the incubation period when most cells were dead. The study of the distribution of individual cells in culture in terms of F_v/F_m parameter, which reflects the quantum yield of PSII photochemistry, revealed the existence of 2–3% of cells retaining high F_v/F_m (>0.7) in the presence of the toxicant. The treated cultures were able to resume growth after prolonged incubation in fresh medium. The high sensitivity fluorescence methods used made it possible to identify stress-resistant cells which maintain high photosynthetic activity in the presence of lethal doses of toxic substances; these cells provide recovery of the population after stress.     

Impact of wavelength and spot size on laser depth of focus: Considerations for mass spectrometry imaging of non-flat samples

Biospecimens with nearly flat surfaces on a flat stage are typically required for laser-based mass spectrometry imaging (MSI) techniques. However, sampling stages are rarely perfectly level, and accounting for this and the need to accommodate non-flat samples requires a deeper understanding of the laser beam depth of focus. In ablation-based MSI methods, a laser is focused on top of the sample surface, ensuring that the sample is at the focal point or remains within depth of focus. In general, the depth of focus of a given laser is related to the beam quality (M²) and the wavelength (λ). However, because laser is applied on a biological sample, other variables can also impact the depth of focus, which could affect the robustness of the MSI techniques for diverse sample types. When the height of a sample ranges outside of the depth of focus, ablated area and the corresponding ion abundances may vary as well, increasing the variability of results. In this tutorial, we examine the parameters and equations that describe the depth of focus of a Gaussian laser beam. Additionally, we describe several approaches that account for surface roughness exceeding the depth of focus of the laser.     

Modulation of Uptake and Reactivity of Nitrogen Dioxide in Metal-Organic Framework Materials

We report the modulation of reactivity of nitrogen dioxide (NO₂) in a charged metal–organic framework (MOF) material, MFM-305-CH₃ in which unbound N-centres are methylated and the cationic charge counter-balanced by Cl⁻ ions in the pores. Uptake of NO₂ into MFM-305-CH₃ leads to reaction between NO₂ and Cl⁻ to give nitrosyl chloride (NOCl) and NO₃⁻ anions. A high dynamic uptake of 6.58 mmol g⁻¹ at 298 K is observed for MFM-305-CH₃ as measured using a flow of 500 ppm NO₂ in He. In contrast, the analogous neutral material, MFM-305, shows a much lower uptake of 2.38 mmol g⁻¹. The binding domains and reactivity of adsorbed NO₂ molecules within MFM-305-CH₃ and MFM-305 have been probed using in situ synchrotron X-ray diffraction, inelastic neutron scattering and by electron paramagnetic resonance, high-field solid-state nuclear magnetic resonance and UV/Vis spectroscopies. The design of charged porous sorbents provides a new platform to control the reactivity of corrosive air pollutants.     

On variants of the Halton sequence

A generalisation of the classical Halton sequence \((\phi _{\beta }(n))_{n\in \mathbb {N}}\) has emerged in recent years based on \(\beta \)-adic expansions of elements of [0, 1). In the case where \(\beta \) is a natural number greater than 1, this reduces to the classical Halton sequence. In this paper, we use ergodic and analytic methods to prove the uniform distribution of a sequence \((\phi _{\beta }(k_j))_{j\in \mathbb {N}}\) for the sequence of integers \((k_j)_{j\ge 0}\), which is both Hartman uniformly distributed and good universal. This builds on earlier work of M. Hofer, M. R. Iaco and R. Tichy in the special case \(k_j =j \ (j=0,1, \ldots )\). Variants of this phenomenon are also studied.     

Using nutritional and oxidative stress to increase content of healthbeneficial fatty acids in oleaginous and non-oleaginous yeasts

Yeast responses to stress conditions include an increase in lipid content and concomitant changes in content of saturated and unsaturated fatty acids. Some fatty acids are among the dietetically important fatty acids and new possibilities are sought for their biotechnological production in addition to those already exploited from marine organisms, nuts and other sources. The possibility of the production of palmitoleic and linoleic acids resulting from new approaches to traditional biotechnologically useful yeast species (Kluyveromyces polysporus, Saccharomyces cerevisiae, Torulospora delbrueckii) and species capable of high accumulation of lipids (Rhodotorula glutinis, Trichosporon cutaneum, Candida sp., Yarrowia lipolytica) was explored. The most promising was the combination of two stress factors: limitation of N-sources (C/N mass ratio of 70: 1) and oxidative stress induced by zero- valent iron nanoparticles. These conditions were conducive to the production of palmitoleic acid commonly used in cosmetics and medicine and ω-6-linoleic acid, a precursor of thromboxanes, prostaglandins and leucotrienes. The yield of these two fatty acids in T. cutaneum was more than 500 mg g^?1 (dry mass) and in Candida sp. more than 600 mg g-1 (dry mass).     

Acetylation Rather than H50Q Mutation Impacts the Kinetics of Cu(II) Binding to α-Synuclein

The interaction between α-synuclein (αSyn) and Cu²⁺ has been suggested to be closely linked to brain copper homeostasis. Disruption of copper levels could induce misfolding and aggregation of αSyn, and thus contribute to the progression of Parkinson's disease (PD). Understanding the molecular mechanism of αSyn-Cu²⁺ interaction is important and controversies in Cu²⁺ coordination geometry with αSyn still exists. Herein, we find that the pathological H50Q mutation has no impact on the kinetics of Cu²⁺ binding to the high-affinity site of wild type αSyn (WT-αSyn), indicating the non-involvement of His50 in high-affinity Cu²⁺ binding to WT-αSyn. In contrast, the physiological N-terminally acetylated αSyn (NAc-αSyn) displays several orders of magnitude weaker Cu²⁺ binding affinity than WT-αSyn. Cu²⁺ coordination mode to NAc-αSyn has also been proposed based on EPR spectrum. In addition, we find that Cu²⁺ coordinated WT-αSyn is reduction-active in the presence of GSH, but essentially inactive towards ascorbate. Our work provides new insights into αSyn-Cu²⁺ interaction, which may help understand the multifaceted normal functions of αSyn as well as pathological consequences of αSyn aggregation.     

The Halton sequence and its discrepancy in the Cantor expansion

Let \(\kappa \) be an infinite cardinal, and \(2^\kappa <\lambda \le 2^{\kappa ^+}\). We prove that if there is a weak diamond on \(\kappa ^+\) then every \(\{C_\alpha :\alpha <\lambda \}\subseteq \mathcal {D}_{\kappa ^+}\) satisfies Galvin’s property. On the other hand, Galvin’s property is consistent with the failure of the weak diamond (and even with Martin’s axiom in the case of \(\aleph _1\)). We derive some consequences about weakly inaccessible cardinals. We also prove that the negation of a similar property follows from the proper forcing axiom.     

Human serum albumin in electrospun PCL fibers: structure,release, and exposure on fiber surface

Human serum albumin (HSA) introduced to the fibers produced by electrospinning from HSA and polycaprolactone (PCL) solutions in hexafluoroisopropanol has been studied in terms of its structure, release from the fibers, stability of interaction with basic polymer, accessibility for protease attack, and cellular receptors, as well as dependence of the studied parameters on the protein concentration in fibers. A limited part of the protein leaves the fibers right after soaking with water, whereas the remaining protein stays tightly bound to fibers for a long time because protein nanoparticles are tightly integrated with PCL, as shown by small‐angle X‐ray scattering. As has been demonstrated, the proteins leave the fibers in complexes with PCL. X‐ray photoelectron spectroscopy demonstrates that the protein concentration on the fiber surface is higher than the concentration in electrospinning solution. The surface‐exposed protein is recognized by cell receptors and is partially hydrolyzed by proteinase K. The data on pulse protein release, presence of PCL in the protein released from matrixes, overrepresentation of the protein on the fiber surface, and tight interaction of protein with PCL may be useful for rational design of electrospun scaffolds intended for drug delivery and tissue engineering. Copyright © 2016 John Wiley & Sons, Ltd.     

The use of physical and virtual infrastructures for the validation of algal cryopreservation methods in international culture collections

Two cryopreservation methods, colligative cryoprotection coupled with controlled cooling and vitrification-based, encapsulation-dehydration were validated by five members of the EU research infrastructure consortium, COBRA, and two independent external validators. The test strain Chlorella vulgaris SAG 211-11b was successfully cryopreserved using two-step cooling employing passive (Mr Frosty) and Controlled Rate Freezers (CRF) attaining the desired recovery target within 15% of the median viability level (94%). Significant differences (p < 0.05) between cooling regimes were observed where Mr Frosty was more variable (Inter-Quartile Range being 21.5%, versus 13.0% for CRF samples). Viability assessment using fluorescein diacetate gave significantly (P < 0.0001) higher survival than growth in agar with median values being 96% and 89%, respectively. On employing encapsulation-dehydration, greater variability between some validators was observed, with six labs observing recovery in 100% of the beads (84-95% of cells surviving) and one lab observing survival in 80% of the treated beads. Bead disruption followed by algal growth in agar was considered the most reliable and accurate method of assessing cell survival for encapsulation-dehydration.