Conformational spread as a mechanism for cooperativity in the bacterial flagellar switch

The bacterial flagellar switch that controls the direction of flagellar rotation during chemotaxis has a highly cooperative response. This has previously been understood in terms of the classic two-state, concerted model of allosteric regulation. Here, we used high-resolution optical microscopy to observe switching of single motors and uncover the stochastic multistate nature of the switch. Our observations are in detailed quantitative agreement with a recent general model of allosteric cooperativity that exhibits conformational spread—the stochastic growth and shrinkage of domains of adjacent subunits sharing a particular conformational state. We expect that conformational spread will be important in explaining cooperativity in other large signaling complexes

«Puss in Boots» by Mykola Hvyleviy: the Peculiarities of the Allusion Space

Стаття містить інтертекстуальний аналіз етюду «Кіт у чоботях» Миколи Хвильового» на рівні алюзії з однойменною літературною казкою Шарля Перро. Досліджено ідейно-естетичні особливості та засоби образо¬творення головних персонажів, обраних за об’єкт дослідження текстів. Визначено функції заголовків творів з урахуванням їх жанрової специфіки. The article contains the intertextual analysis of the essay «Puss in Boots» by M. Hvyleviy and similarly-named literary fairy tale by Ch. Perrault at allusion-level. Notionally-aesthetic peculiarities and the devices of image-making of the main characters, taken as the objects of the specific of the genre, are pointed out

Hidden Stochastic Nature of a Single Bacterial Motor

The rotary flagellar motor of Escherichia coli bacterium switches stochastically between the clockwise (CW) and counterclockwise (CCW) direction. We found that the CW and CCW intervals could be described by a gamma distribution, suggesting the existence of hidden Markov steps preceding each motor switch. Power spectra of time series of switching events exhibited a peaking frequency instead of the Lorentzian profile expected from standard kinetic two-state models. Our analysis indicates that the number of hidden steps may be a key dynamical parameter underlying the switching process in a single bacterial motor as well as in large cooperative molecular systems.Molecular and Cellular BiologyPhysic

Beyond the frame rate: Measuring high-frequency fluctuations with light intensity modulation

Power spectral density measurements of any sampled signal are typically restricted by both acquisition rate and frequency response limitations of instruments, which can be particularly prohibitive for video-based measurements. We have developed a new method called Intensity Modulation Spectral Analysis (IMSA) that circumvents these limitations, dramatically extending the effective detection bandwidth. We demonstrate this by video-tracking an optically-trapped microsphere while oscillating an LED illumination source. This approach allows us to quantify fluctuations of the microsphere at frequencies over 10 times higher than the Nyquist frequency, mimicking a significantly higher frame rate.Comment: 4 pages, 2 figure

Relationship between cellular response and behavioral variability in bacterial chemotaxis

Bacterial chemotaxis in Escherichia coli is a canonical system for the study of signal transduction. A remarkable feature of this system is the coexistence of precise adaptation in population with large fluctuating cellular behavior in single cells (Korobkova et al. 2004, Nature, 428, 574). Using a stochastic model, we found that the large behavioral variability experimentally observed in non-stimulated cells is a direct consequence of the architecture of this adaptive system. Reversible covalent modification cycles, in which methylation and demethylation reactions antagonistically regulate the activity of receptor-kinase complexes, operate outside the region of first-order kinetics. As a result, the receptor-kinase that governs cellular behavior exhibits a sigmoidal activation curve. This curve simultaneously amplifies the inherent stochastic fluctuations in the system and lengthens the relaxation time in response to stimulus. Because stochastic fluctuations cause large behavioral variability and the relaxation time governs the average duration of runs in response to small stimuli, cells with the greatest fluctuating behavior also display the largest chemotactic response. Finally, Large-scale simulations of digital bacteria suggest that the chemotaxis network is tuned to simultaneously optimize the random spread of cells in absence of nutrients and the cellular response to gradients of attractant.Comment: 15 pages, 4 figures, Supporting information available here http://cluzel.uchicago.edu/data/emonet/arxiv_070531_supp.pd

The Russian press headlines denoting China

This article discusses the newspaper headlines of Russian mass newspapers ("Arguments and facts", "Komsomolskaya Pravda"). It is not a secret that the impact of printed information flows surpasses the influence of all other types of mass media: radio, television, Internet resources. The language of articles is an indicator of the processes taking place in different areas of the Russian language. Recently journalists have observed the strengthening of Russian-Chinese relations. As a result - the emergence of a large number of articles about the life of the neighboring country. The aim of the work is to study the headlines denoting Chin

The Aerotactic Response of Caulobacter crescentus

Many motile microorganisms are able to detect chemical gradients in their surroundings to bias their motion toward more favorable conditions. In this study, we observe the swimming patterns of Caulobacter crescentus, a uniflagellated bacterium, in a linear oxygen gradient produced by a three-channel microfluidic device. Using low-magnification dark-field microscopy, individual cells are tracked over a large field of view and their positions within the oxygen gradient are recorded over time. Motor switching events are identified so that swimming trajectories are deconstructed into a series of forward and backward swimming runs. Using these data, we show that C. crescentus displays aerotactic behavior by extending the average duration of forward swimming runs while moving up an oxygen gradient, resulting in directed motility toward oxygen sources. Additionally, the motor switching response is sensitive both to the steepness of the gradient experienced and to background oxygen levels, exhibiting a logarithmic response

KVINNORS UPPLEVELSER UNDER KLIMAKTERIET En litteraturstudie om kvinnors upplevelser under klimakteriet.

Bakgrund: Klimakteriet är en naturlig fas i kvinnors liv som resulterar i hormonella och fysiologiska förändringar i kroppen. Dessa förändringar leder till flera vanligt förekommande symtom, såsom värmevallningar, viktförändringar och psykiska besvär. Övergångsperioden omfattar en stor del av kvinnans liv, så det är nödvändigt att bemöta och stötta kvinnor på ett professionellt sätt. Syfte: Syftet med studien är att belysa hur kvinnor upplever klimakteriet. Metod: En litteraturöversiktsstudie med induktiv ansats valdes för att analysera 8 vetenskapliga artiklar, varav 7 använde kvalitativa metoder och 1 använde kvantitativ metod. Resultat: Resultatet visar hur kvinnor upplever övergångsfasen, som kategoriserades i två huvudteman: osäkerhet vid klimakteriet och vårdupplevelser. Slutsats: Kvinnor upplever klimakteriet på olika sätt vad gäller symtom och förväntningar från vården. Både kvinnor och sjukvårdspersonal behöver öka sin kunskap om övergångsåldern. Sjukvårdspersonalens kunskapsutveckling bör ge möjlighet att jobba med patienten på ett personcentrerad och individanpassat sätt, så att kvinnor känner sig hörda och bekräftade under övergångsperioden

Phenotypic Variation and Bistable Switching in Bacteria

Microbial research generally focuses on clonal populations. However, bacterial cells with identical genotypes frequently display different phenotypes under identical conditions. This microbial cell individuality is receiving increasing attention in the literature because of its impact on cellular differentiation, survival under selective conditions, and the interaction of pathogens with their hosts. It is becoming clear that stochasticity in gene expression in conjunction with the architecture of the gene network that underlies the cellular processes can generate phenotypic variation. An important regulatory mechanism is the so-called positive feedback, in which a system reinforces its own response, for instance by stimulating the production of an activator. Bistability is an interesting and relevant phenomenon, in which two distinct subpopulations of cells showing discrete levels of gene expression coexist in a single culture. In this chapter, we address techniques and approaches used to establish phenotypic variation, and relate three well-characterized examples of bistability to the molecular mechanisms that govern these processes, with a focus on positive feedback.