Temperature factor and magnetic noise under conditions of stochastic resonance of magnetosomes

The influence of magnetic noise on the dynamics of magnetic nanoparticles under stochastic resonance conditions is considered. The effect of magnetic noise on the nanoparticles at a fixed actual ambient temperature is equivalent to an increase in the effective temperature of the thermostat. This observation may be used to test whether magnetic nanoparticles are involved in the biological effects of weak magnetic fields.     

The stochastic resonance of magnetosomes fixed in the cytoskeleton

The rotation of microscopic magnetic particles, magnetosomes, embedded into the cytoskeleton and subjected to a magnetic field and thermal noise was considered. The dynamics of magnetosome is shown to comply with the conditions of the stochastic resonance under not too tight constraints on the character of particle fastening. The excursion of regular rotations attains the value of the order of radian, which facilitates explaining the biological effects of low-frequency weak magnetic fields and geomagnetic fluctuations.     

Dielectric measurements on live biological materials under magnetic resonance conditions

In the course of work on the interactions of electric and magnetic fields with both living and dead biological materials, it was noticed that certain published dielectrophoretic yield curves for biological cells showed unexplained deviations in the region of 2 kHz. Dielectrophoretic measurements made at frequencies and magnetic fields which satisfied the nuclear magnetic resonance conditions showed sharply resonant features. Dielectric measurements showed small, but sharp, resonances most easily seen in the dielectric loss curves which had a bandwidth of the order of one Hertz and presented at the frequencies which satisfied the magnetic resonance conditions for the ambient magnetic field. Resonances were found corresponding to the frequencies for electron spin resonance and nuclear magnetic resonance for¹H,³¹P,²³Na,³⁷Cl and³⁹K. The onset of these resonances occurs at the value of the steady magnetic field strength so that one quantum of magnetic flux (2.07×10^?15wb) would link a single biological cell or pair of cells, approximately 1 G (100μT) in the case of a 5-μm yeast cell. The effects of these magnetic resonance conditions on the mean generation time ofE. coli and on the reaction of the enzyme lysozyme with the substrateM. lysodeikticus cells are also shown.     

23Na-nuclear magnetic resonance investigation of gramicidin-induced ion transport through membranes under equilibrium conditions.

A technique for investigating the gramicidin-facilitated transport of Na+ ions across lipid bilayers of large unilamellar vesicles under the condition of ionic equilibrium has been developed using a combination of heat incubation of the gramicidin with the vesicles and 23Na-nuclear magnetic resonance (NMR) spectroscopy. Isolation of the two 23Na-NMR signals from the intra- and extravesicular Na+ with the shift reagent, dysprosium (III) tripolyphosphate, allows the equilibrium flux of Na+ through the gramicidin channels to be detected and treated as a two-site exchange process. This study indicates that the transport of Na+ through gramicidin channels is second order with respect to the gramicidin concentration.     

The presence of both stochastic and deterministic dynamics in electroretinograms measured under identical experimental conditions

We have studied whether living things investigated under the same measuring conditions can generate signals with different types of dynamics. We also wanted to detect the possible effects of low-intensity microwaves using parameters of deterministic chaos. For this purpose, two sets of electroretinograms were analysed by methods aimed at recognizing different types of dynamics. Both sets included the time series recorded from objects exposed to low-intensity microwaves and those that were not exposed. The analytical methods are based on nonlinear forecasting and a “surrogate data” technique. Although the experimental conditions were identical for the two sets, we have shown that both have time series with deterministic and stochastic dynamics. We also found that the use of parameters of deterministic dynamics is insufficient to distinguish between the sets. Received: 18 January 1994 / Accepted: 13 June 1997     

Peculiarities of charged particle dynamics under cyclotron resonance conditions

Peculiarities of the dynamics of charged particles interacting with electromagnetic radiation under nearly autoresonance conditions are analyzed. In particular, analysis of nonlinear cyclotron resonances shows that their widths increase when the autoresonance conditions are approached. In this case, however, the distance between nonlinear resonances increases even faster, due to which nonlinear resonances do not overlap and, accordingly, regimes with dynamic chaos do not occur. According to calculations, the dynamics of charged particles under the autoresonance conditions is very sensitive to fluctuations, the effect of which can be anomalously large and lead to superdiffusion. It is shown that, under the autoresonance conditions, particle dynamics on small time intervals can differ significantly from that on large time intervals. This effect is most pronounced in the presence of fluctuations in the system.     

The immunological reactions of fishes to parasite infection under different temperature conditions

The dependence of immunological reactions of fishes infected with Ichthyophthirius multifiliis infusoria was elucidated. The invasion of the parasite results in the activation of the immune system, increased phagocytosis and a growth of the activity of oxydase enzymes. With the increased number and sizes of parasites a decrease of the above parameters below the control values is observed. Changes of the immunological values are most dynamic at high (20-25 degrees) and they are slower at low (10 degrees) temperatures.     

The effects of reversibility and noise on stochastic phosphorylation cycles and cascades

The phosphorylation-dephosphorylation cycle is a common motif in cellular signaling networks. Previous work has revealed that, when driven by a noisy input signal, these cycles may exhibit bistable behavior. Here, a recently introduced theorem on network bistability is applied to prove that the existence of bistability is dependent on the stochastic nature of the system. Furthermore, the thermodynamics of simple cycles and cascades is investigated in the stochastic setting. Because these cycles are driven by the ATP hydrolysis potential, they may operate far from equilibrium. It is shown that sufficient high ATP hydrolysis potential is necessary for the existence of a bistable steady state. For the single-cycle system, the ensemble average behavior follows the ultrasensitive response expected from analysis of the corresponding deterministic system, but with significant fluctuations. For the two-cycle cascade, the average behavior begins to deviate from the expected response of the deterministic system. Examination of a two-cycle cascade reveals that the bistable steady state may be either propagated or abolished along a cascade, depending on the parameters chosen. Likewise, the variance in the response can be maximized or minimized by tuning the number of enzymes in the second cycle.     

Influence of the bacterial growth phase on the magnetic properties of magnetosomes synthesized by Magnetospirillum gryphiswaldense

Background: The magnetosome biosynthesis is a genetically controlled process but the physical properties of the magnetosomes can be slightly tuned by modifying the bacterial growth conditions.Methods: We designed two time-resolved experiments in which iron-starved bacteria at the mid-logarithmic phase are transferred to Fe-supplemented medium to induce the magnetosomes biogenesis along the exponential growth or at the stationary phase. We used flow cytometry to determine the cell concentration, transmission electron microscopy to image the magnetosomes, DC and AC magnetometry methods for the magnetic characterization, and X-ray absorption spectroscopy to analyze the magnetosome structure.Results: When the magnetosomes synthesis occurs during the exponential growth phase, they reach larger sizes and higher monodispersity, displaying a stoichiometric magnetite structure, as fingerprinted by the well defined Verwey temperature. On the contrary, the magnetosomes synthesized at the stationary phase reach smaller sizes and display a smeared Verwey transition, that suggests that these magnetosomes may deviate slightly from the perfect stoichiometry.Conclusions: Magnetosomes magnetically closer to stoichiometric magnetite are obtained when bacteria start synthesizing them at the exponential growth phase rather than at the stationary phase.General significance: The growth conditions influence the final properties of the biosynthesized magnetosomes. This article is part of a Special Issue entitled “Recent Advances in Bionanomaterials” Guest Editors: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.     

不同温度条件下霍乱弧菌生存能力的实验研究

目的通过在不同温度条件下对霍乱弧菌生存能力的观察,探索大连市水域中霍乱弧菌在流行＂间歇期＂如何存活和越冬。方法在自然海水和湖水中分别接种本市分离出的埃尔托型霍乱弧菌流行株小川1b型（大E940014）和埃尔托型霍乱弧菌非流行株小川32l（大E940011）,在1～2℃、5～6℃及10～12℃3个温度条件下检测霍乱弧菌生存能力。结果流行株（小川1b型）在1～2℃海水存活26 d,5～6℃存活28 d,10～12℃存活46 d。可见,10～12℃生存时间明显高于1～2℃或5～6℃（P〈0.05）。结论两类菌株的生存对环境温度均很敏感,温度越低死亡越快。在自然水体中,非流行株生存时间略长于流行株;而在除菌水体中两类菌存活能力基本一致。     

Effect of temperature on seedling growth under impeding conditions

Studies were carried out under controlled laboratory conditions to evaluate the seedling growth capacities of chickpea (Cicer arietinum L.) varieties Pusa 209 and H208 at constant temperatures of 15, 20, 25 and 28°C (±0.5°C) and of pigeonpea (Cajanus cajan L.) variety Prabhat at 20 and 28°C (±0.5°C). Seedling growth at any given time was found to depend on ‘a’, the growth at no impedance, and ‘b’, the impedance growth factori.e., decrease in growth with increase in impedance, and on temperature. The optimum temperature for chickpea was found to be in the range of 20 to 24°C for better seedling growth characteristics, whereas for pigeonpea, 28°C was found to be more congenial than 20°C. Chickpea varieties differed in their response to temperature. Part of the M. Sc. thesis of first author submitted to the Indian Agricultural Research Institute, New Delhi-110012, India.     

Monophyletic origin of magnetotaxis and the first magnetosomes

Horizontal gene transfer (HGT), the transfer of genetic material other than by descent, is thought to have played significant roles in the evolution and distribution of genes in prokaryotes. These include those responsible for the ability of motile, aquatic magnetotactic bacteria (MTB) to align and swim along magnetic field lines and the biomineralization of magnetosomes that are responsible for this behaviour. There is some genomic evidence that HGT might be responsible for the distribution of magnetosome genes in different phylogenetic groups of bacteria. For example, in the genomes of a number of MTB, magnetosome genes are present as clusters within a larger structure known as the magnetosome genomic island surrounded by mobile elements such as insertion sequences and transposases as well as tRNA genes. Despite this, there is no strong direct proof of HGT between these organisms. Here we show that a phylogenetic tree based on magnetosome protein amino acid sequences from a number of MTB was congruent with the tree based on the organisms' 16S rRNA gene sequences. This shows that evolution and divergence of these proteins and the 16S rRNA gene occurred similarly. This suggests that magnetotaxis originated monophyletically in the Proteobacteria phylum and implies that the common ancestor of all Proteobacteria was magnetotactic.     

Rectal temperature of the husky under severe winter conditions in the Antarctic

Rectal temperatures were measured in a group of 15 huskies during the Antarctic winter at Halley Bay, and found to vary between37–55 and 40 25^oC. A significant positive correlation was shown between ambient and the mean rectal temperatures. It is suggested that the dogs'reaction to the cold environment shows a possible acclimatization effect.     

Conformational analysis of thyrotropin releasing factor by proton magnetic resonance spectroscopy

The proton magnetic resonance spectrum of thyrotropin releasing factor (TRF) in solution in deuterium oxide and deuterated dimethylsulfoxide (DMSO–d₆) has been analyzed. Two forms differing in cis–trans isomerism about the His-Pro peptide bond are observed. From the temperature dependence of chemical shift of the amide protons, it is concluded that TRF in DMSO–d₆ does not contain intramolecular hydrogen bonds. Measurement of NH? C_αH coupling constant provides an estimate of the histidine dihedral angle ?. Structural information about the histidine side-chain is deduced from C_αH? C_βH coupling constants and from the nonequivalence of the two prolyl δ-protons. In DMSO–d₆, there is evidence for a tautomeric equilibrium corresponding to an exchange of imidazole proton between the two nitrogen atoms N-δ and N-ε. In water, the N-εH tautomer is found to be the predominant tautomeric form of the imidazole ring. These results in combination with energy calculation, vibrational analysis, and carbon nmr studies allow the determination of the conformationof TRF.