Quorum Sensing及其研究进展

Quomm sensing(QS)是近来受到广泛关注的一种细菌群体行为调控机制．由于不少人体或植物病原菌的发病机制受QS机制的调控,很多细菌代谢产物也受到该机制的控制,QS系统已成为医学、生物工程学等多领域的研究热点,在QS的调控过程中,细菌分泌一种或多种自诱导剂(autoinducer,也称信息素pheromone),然后通过感应     

Sensing acidosis: nociception or sngception?

Background

Sensing tissue acidosis is an important function of the somatosensory nervous system to response to noxious stimuli.

Main body

In the pain clinic, acid or soreness sensation is a characteristic sensory phenotype of various acute and chronic pain syndromes, such as delayed onset muscle soreness, fibromyalgia, and radicular pain. However, soreness sensation is a sign of successful analgesia for acupuncture and noxipoint therapy. Thus, the nature of acid or soreness sensation is not always nociceptive (or painful) and could be anti-nociceptive. To facilitate the investigation of the molecular and neurobiological mechanisms of soreness sensation, we propose a concept called “sngception (sng- ception)” to describe the response of the somatosensory nervous system to sense tissue acidosis and to distinguish it from nociception. “Sng” is a Taiwanese word that represents the state of soreness while at the same time imitates the natural vocalization of humans feeling sore.

Conclusion

Here we propose sngception as a specific somatosensory function that transmits the acid sensation from the peripheral to the central nervous system. Sngception could partially overlap with nociception, but it could also transmit antinociception, proprioception, and pruriception.

     

Mangroves of Godavari – Analysis Through Remote Sensing Approach

The expansion of agriculture and aquaculture farms in the coastal areas has led to conversion of mangroves in the recent past. The extent of mangroves has also changed due to the erosion of mangroves along the coast and accretion near river mouths, leading to the formation of new mangrove areas. This study has been undertaken in the mangroves of the Godavari estuary, Andhra Pradesh, India to understand the changes in the extent of mangroves, namely accreted mangroves, erosion due to wave action and river water flow during floods, and changes due to forest restoration between 1986 and 2001, through remote sensing. The geomorphological changes due to river water flow in and around the mangroves have also been analysed. The changes in the vegetation due to forest restoration and natural regeneration are appreciable, while the changes in the area due to erosion and accretion are more or less equal. An analysis of the remote sensing images of 1986 and 2001 reveal that the mangroves outside the forest boundary have been converted to aquaculture. The sand spit of Hope Island has changed with time and has grown nearly 2.6 km between 1937 and 2001.     

Fluid–Structure Interaction-Based Biomechanical Perception Model for Tactile Sensing

The reproduced tactile sensation of haptic interfaces usually selectively reproduces a certain object attribute, such as the object''s material reflected by vibration and its surface shape by a pneumatic nozzle array. Tactile biomechanics investigates the relation between responses to an external load stimulus and tactile perception and guides the design of haptic interface devices via a tactile mechanism. Focusing on the pneumatic haptic interface, we established a fluid–structure interaction-based biomechanical model of responses to static and dynamic loads and conducted numerical simulation and experiments. This model provides a theoretical basis for designing haptic interfaces and reproducing tactile textures.     

Quorum Sensing,or How Bacteria “Talk” to Each Other

Reviewed are recent advances in studying the quorum-sensing systems, which regulate gene expression depending on population density. Low-molecular-weight acyl derivatives of L-homoserine lactone (N-AHL) freely diffuse through cell membranes and determine cell-to-cell communication in bacteria. The quorum-sensing systems have first been found to regulate bioluminescence in marine bacteria Photobacterium(Vibrio) fischeriand Vibrio harveyi. Such systems are widespread and control expression of genes for virulence factors, proteases, antibiotics, etc., in various Gram-negative bacteria, including plant, animal, and human pathogens. Quorum sensing is a prominent example of social behavior in bacteria, as signal exchange among individual cells allows the entire population to choose an optimal way of interaction with the environment and with higher organisms.     

The Influence of Fluid Flow on Modeling Quorum Sensing in Bacterial Biofilms

In this paper, we study quorum sensing in Pseudomonas aeruginosa biofilms. Quorum sensing is a process where bacteria monitor their population density through the release of extra-cellular signalling molecules. The presence of these molecules affects gene modulation leading to changes in behaviour such as the release of virulence factors. Here, we use numerical methods to approximate a 2-D model of quorum sensing. It is observed that the shape of the biofilm can have a profound effect on the onset of quorum sensing. This has serious repercussions for experimental observations since biofilms of the same biomass but different shapes can produce quite different results.     

Analyzing Thermal Stability of Cell Membrane of Salmonella Using Time-Multiplexed Impedance Sensing

Heat treatment is one of the most widely used methods for inactivation of bacteria in food products. Heat-induced loss of bacterial viability has been variously attributed to protein denaturation, oxidative stress, or membrane leakage; indeed, it is likely to involve a combination of these processes. We examine the effect of mild heat stress (50–55°C for ≤12 min) on cell permeability by directly measuring the electrical conductance of samples of Salmonella enterica serovar Typhimurium to answer a fundamental biophysical question, namely, how bacteria die under mild heat stress. Our results show that when exposed to heat shock, the cell membrane is damaged and cells die mainly due to the leakage of small cytoplasmic species to the surrounding media without lysis (confirmed by fluorescent imaging). We measured the conductance change, ΔY, of wild-type versus genetically modified heat-resistant (HR) cells in response to pulse and ramp heating profiles with different thermal time constants. In addition, we developed a phenomenological model to correlate the membrane damage, cytoplasmic leakage, and cell viability. This model traces the differential viability and ΔY of wild-type and HR cells to the difference in the effective activation energies needed to permeabilize the cells, implying that HR cells are characterized by stronger lateral interactions between molecules, such as lipids, in their cell envelope.     

Sensing Domain Dynamics in Protein Kinase A-I�� Complexes by Solution X-ray Scattering

The catalytic (C) and regulatory (R) subunits of protein kinase A are exceptionally dynamic proteins. Interactions between the R- and C-subunits are regulated by cAMP binding to the two cyclic nucleotide-binding domains in the R-subunit. Mammalian cells express four different isoforms of the R-subunit (RIα, RIβ, RIIα, and RIIβ) that all interact with the C-subunit in different ways. Here, we investigate the dynamic behavior of protein complexes between RIα and C-subunits using small angle x-ray scattering. We show that a single point mutation in RIα, R333K (which alters the cAMP-binding properties of Domain B) results in a compact shape compared with the extended shape of the wild-type R·C complex. A double mutant complex that disrupts the interaction site between the C-subunit and Domain B in RIα, RIα_ABR333K·C(K285P), results in a broader P(r) curve that more closely resembles the P(r) profiles of wild-type complexes. These results together suggest that interactions between RIα Domain B and the C-subunit in the RIα·C complex involve large scale dynamics that can be disrupted by single point mutations in both proteins. In contrast to RIα·C complexes. Domain B in the RIIβ·C heterodimer is not dynamic and is critical for both inhibition and complex formation. Our study highlights the functional differences of domain dynamics between protein kinase A isoforms, providing a framework for elucidating the global organization of each holoenzyme and the cross-talk between the R- and C-subunits.     

Temperature Sensing by Plants: Calcium-Permeable Channels as Primary Sensors—A Model

Recently the properties of temperature sensing in plants have been demonstrated experimentally by Plieth et al. (The Plant Journal 1999. 18:491–497). The relevant biophysical parameters are established here by mathematical modeling in order to understand the experimental findings in quantitative terms. A simple one-compartment model is presented, as a preliminary approach to explain how the input signal (i.e., temperature T) is perceived and how the information is translated into an output signal in the plant cell (i.e., [Ca²⁺] _c ). The model is based on the fact that calcium influx into the cytoplasm is mediated by calcium-permeable channels which are assumed to be solely dependent on cooling rate (dT/dt) and calcium efflux is mediated by calcium pumps which have been shown to be dependent on absolute temperature (T). Firstly, it is demonstrated that this model is able to meet the demand for a satisfactory interpretation of the experimental data, and secondly that it reproduces the experimentally observed features of the cooling induced [Ca²⁺] _c changes well. This suggests that the primary temperature sensor in plants might be a Ca²⁺-permeable channel. Received: 4 June 1999/Revised: 26 July 1999     

How do I begin? Sensing extracellular stress to maintain yeast cell wall integrity

The cell wall integrity (CWI) signalling pathway is necessary to remodel the yeast cell wall during normal morphogenesis and in response to cell surface stress. In the Baker's yeast Saccharomyces cerevisiae, a set of five membrane-spanning sensors, namely Wsc1, Wsc2, Wsc3, Mid2 and Mtl1, detect perturbations in the cell wall and/or the plasma membrane and activate a downstream signal transduction pathway with a central MAP kinase module. As a consequence, the expression of genes whose products are involved in cell wall structure and remodelling is induced. This review summarises our recent results on sensor structure and function, as well as the advances made regarding sensor mechanics.     

Direct Fe2+ Sensing by Iron-responsive Messenger RNA��Repressor Complexes Weakens Binding

Fe²⁺ is now shown to weaken binding between ferritin and mitochondrial aconitase messenger RNA noncoding regulatory structures ((iron-responsive element) (IRE)-RNAs) and the regulatory proteins (IRPs), which adds a direct role of iron to regulation that can complement the well known regulatory protein modification and degradative pathways related to iron-induced mRNA translation. We observe that the K_d value increases 17-fold in 5′-untranslated region IRE-RNA·repressor complexes; Fe²⁺, is studied in the absence of O₂. Other metal ions, Mn²⁺ and Mg²⁺ have similar effects to Fe²⁺ but the required Mg²⁺ concentration is 100 times greater than for Fe²⁺ or Mn²⁺. Metal ions also weaken ethidium bromide binding to IRE-RNA with no effect on IRP fluorescence, using Mn²⁺ as an O₂-resistant surrogate for Fe²⁺, indicating that metal ions bound IRE-RNA but not IRP. Fe²⁺ decreases IRP repressor complex stability of ferritin IRE-RNA 5–10 times compared with 2–5 times for mitochondrial aconitase IRE-RNA, over the same concentration range, suggesting that differences among IRE-RNA structures contribute to the differences in the iron responses observed in vivo. The results show the IRE-RNA·repressor complex literally responds to Fe²⁺, selectively for each IRE-mRNA.Iron (e.g. ferrous sulfate, ferric citrate, and hemin) added to animal cells changes translation rates of messenger RNAs encoding proteins of iron traffic and oxidative metabolism (1–4). To cross cell membranes, iron ions are transported by membrane proteins such as DMT1 or carried on proteins such as transferrin. Inside the cells, iron is mainly in heme, FeS clusters, non-heme iron cofactors of proteins, and iron oxide minerals coated by protein nanocages (ferritins). Iron in transit is thought to be Fe²⁺ in labile “pools” accessible to small molecular weight chelators, and/or bound loosely by chaperones.When iron concentrations in the cells increase, a group of mRNAs with three-dimensional, noncoding structures in the 5′-untranslated region (UTR)³ are derepressed (Fig. 1A), i.e. the fraction of the mRNAs in mRNA·repressor protein complexes, which inhibit ribosome binding, decreases and the fraction of the mRNAs in polyribosomes increases (5–7). The three-dimensional, noncoding mRNA structure, representing a family of related structures, is called the iron-responsive element, or IRE, and the repressors are called iron regulatory proteins (IRPs). Together they are one of the most extensively studied eukaryotic messenger RNA regulatory systems (1–4). In addition to large numbers of cell studies, structures of IRE-RNAs are known from solution NMR (8–12), and the RNA·protein complex from x-ray crystallography (13). Recent data indicate that demetallation of IRP1 and disruption of the [4Fe-4S] cluster that inhibits IRP1 binding to RNA will be enhanced by phosphorylation and low iron concentrations (1, 2, 14–16). Such results can explain the increased IRP1 binding to IRE-mRNAs and increased translational repression when iron concentrations are abnormally low. However, the mechanism to explain dissociation of IRE-RNA·IRP complexes, thereby allowing ribosome assembly and increased proteosomal degradation of IRPs (1, 2, 14, 15) (Fig. 1A), when high iron concentrations are abnormally high, is currently unknown.Open in a separate windowFIGURE 1.IRE-RNA·IRP complexes and a model for depression by excess iron. A, a representative model of iron-induced translation of 5′-UTR IRE-RNAs. This figure is modified from Ref. 7. B, IRE-RNA sites influenced by metal binding related to the crystal structure of the ferritin-IRE-RNA·IRP complex from Ref. 13. The figure was created by T. Tosha using Discovery Studio 1.6 and Protein Data Bank file 2IPY. ■, hydrated Mg²⁺, determined by solution NMR; ▴, Cu¹⁺-1.10-phenanthroline, determined by RNA cleavage in O₂.Metal ion binding changes conformation and function of most RNA classes, e.g. rRNA (17), tRNA (18, 19), ribozymes (20–23), riboswitches (24, 25), possibly hammerhead mRNAs in mammals (26), and proteins. Although the effects of metal ion binding on eukaryotic mRNAs have not been extensively studied, Mg²⁺ is known to cause changes in conformation, shown by changes in radical cleavage sites of IRE-RNA with 1,10-phenanthrolene-iron and proton shifts in the one-dimensional NMR spectrum (12, 27). The Mg²⁺ effects are observed at low magnesium concentrations (0.1–0.5 mm) and low molar stoichiometries (1:1 and 2:1 = Mg:RNA).We hypothesized that Fe²⁺ could directly change the binding of the IRE-mRNA to the iron regulatory protein for several reasons. First, other metal ions influence the IRE-RNA structure (12, 27). Second, in IRE-RNA/IRP cocrystals there are exposed RNA sites in the IRE-RNA/IRP complex that are accessible for interactions (13) (Fig. 1B). Third, regions in the IRE-RNA are hypersensitive to Fe²⁺-EDTA/ascorbate/H₂O₂, suggesting selective interactions with metals and/or solvent (28). We now report that Fe²⁺ weakens IRE-RNA/IRP binding, whereas Mg²⁺ requires 100 times the concentration and Mn²⁺ is comparable with Fe²⁺; the Fe²⁺ effect was diminished in mutant IRE-RNA and IRE-RNA selective in wild type sequences: ferritin IRE-RNA > mt-aconitase IRE-RNA.     

Approaching the Next Revolution? Evolutionary Integration of Neural and Immune Pathogen Sensing and Response

Mammalian immunity evolved by the process of natural selection that produced differential survival and reproduction advantages through combinations of hereditary traits underlying the response to pathogens. Primitive animals sense the presence of microbial pathogens through recognition of pathogen-derived molecules in their rudimentary immune and nervous systems. No molecular biological mechanism assigns primacy of pathogen sensing mechanisms to immune cells over neurons. Rather, in animals as diverse as Caenorhabditis elegans to mammals, neural reflexes are activated by the presence of pathogens and transduce neural mechanisms that control the development of immunity. A coming revolution in immunological thinking will require immunologists to incorporate neural circuits into understanding pathogen signal transduction, and the molecular mechanisms of learning, that culminate in immunity.On considering memory, one finds an ironic perspective, tainted by shadows of two major scientific fields that, historically at least, did not collaborate. Immunological memory, mediated by lymphocytes, and neurological memory, mediated by neurons, evolved over millions of years in response to environmental changes. Closer inspection within both fields reveals key features of common origin between neural and immune information collection and retrieval. Major evolutionary advantages arose at points of intersection of these systems, manifested as beneficial physiological responses to environmental stimuli during infection, injury, and metabolic stress. In 1989, Charles Janeway proposed that the first revolution in immunological thinking led to the domination of the humoral theory of immunity, and that an approaching second revolution would integrate innate and adaptive immunity by understanding the role of pathogen-associated molecular pattern receptors (Janeway 1989). Today, I believe that the groundwork has been laid for a third revolution in immunological thinking that will integrate the role of neurological feedback circuits into innate and adaptive immunity, including the role of molecular mechanisms through which neurons sense microbes and regulate the output of hematopoietic-derived immune cells. I also suggest that costimulation of neural reflex circuits by microbial products plays a major role in the immune response to infection, and to the subsequent development of immunity (Fig. 1). If correct, this idea could revolutionize our thinking about immunity and take us beyond innate and adaptive immunity to an integrated view of neurological and immunological recognition and learning.Open in a separate windowFigure 1.Pathogens or products of cellular inflammation and injury costimulate immune cells and neurons during the earliest stages of infection. Neural input activates reflex circuits, which modulate the nervous system and the immune system. Hematopoietic-derived cellular responses produce humoral and cellular signals that influence immune cells and neurons. These signal transduction pathways culminate in mediating the behavior of the animal and in initiating learning.     

Cytosolic Nitrate Ion Homeostasis: Could it Have a Role in Sensing Nitrogen Status?

BACKGROUND AND AIMS: question of whether homeostasis occurs for some nutrients and, if so, what are the consequences for how plants sense their nutrient status. Particularly for nitrate, this controversy has focused on the methods used and the cellular pools which they measure. Cytoplasm and cytosol have been distinguished and it has been suggested that two ranges of nitrate values can be separated depending on whether the method separates the pools found in organelles. SCOPE: The present study defines homeostasis of nutrient ions and discusses how whole organ averaging techniques can hide important cellular differences that can help to explain some of the discrepancies between results reported by various methods. These results are considered in relation to a possible role in signalling nutrient status, and have relevance to other averaging techniques such as the use of 'omics' technologies.     

Can We Disrupt the Sensing of Honey Bees by the Bee Parasite Varroa destructor?

BackgroundThe ectoparasitic mite, Varroa destructor, is considered to be one of the most significant threats to apiculture around the world. Chemical cues are known to play a significant role in the host-finding behavior of Varroa. The mites distinguish between bees from different task groups, and prefer nurses over foragers. We examined the possibility of disrupting the Varroa – honey bee interaction by targeting the mite''s olfactory system. In particular, we examined the effect of volatile compounds, ethers of cis 5-(2′-hydroxyethyl) cyclopent-2-en-1-ol or of dihydroquinone, resorcinol or catechol. We tested the effect of these compounds on the Varroa chemosensory organ by electrophysiology and on behavior in a choice bioassay. The electrophysiological studies were conducted on the isolated foreleg. In the behavioral bioassay, the mite''s preference between a nurse and a forager bee was evaluated.ConclusionsThese data indicate the potential of the selected compounds to disrupt the Varroa - honey bee associations, thus opening new avenues for Varroa control.     

The IRP1-HIF-2α Axis Coordinates Iron and Oxygen Sensing with Erythropoiesis and Iron Absorption

1. Download : Download high-res image (158KB)
2. Download : Download full-size image

Highlights? Derepression of HIF-2α mRNA in Irp1^?/? mice causes age-dependent polycythemia ? HIF-2α hyperactivity is observed in multiple tissues of Irp1^?/? mice ? The mRNA regulons of IRP1 and IRP2 are separable in vivo ? The IRP1-HIF-2α axis is a therapeutic target for hematologic or oncologic disorders     

Measuring 3D Hand and Finger Kinematics—A Comparison between Inertial Sensing and an Opto-Electronic Marker System

Objective analysis of hand and finger kinematics is important to increase understanding of hand function and to quantify motor symptoms for clinical diagnosis. The aim of this paper is to compare a new 3D measurement system containing multiple miniature inertial sensors (PowerGlove) with an opto-electronic marker system during specific finger tasks in three healthy subjects. Various finger movements tasks were performed: flexion, fast flexion, tapping, hand open/closing, ab/adduction and circular pointing. 3D joint angles of the index finger joints and position of the thumb and index were compared between systems. Median root mean square differences of the main joint angles of interest ranged between 3.3 and 8.4deg. Largest differences were found in fast and circular pointing tasks, mainly in range of motion. Smallest differences for all 3D joint angles were observed in the flexion tasks. For fast finger tapping, the thumb/index amplitude showed a median difference of 15.8mm. Differences could be explained by skin movement artifacts caused by relative marker movements of the marker system, particularly during fast tasks; large movement accelerations and angular velocities which exceeded the range of the inertial sensors; and by differences in segment calibrations between systems. The PowerGlove is a system that can be of value to measure 3D hand and finger kinematics and positions in an ambulatory setting. The reported differences need to be taken into account when applying the system in studies understanding the hand function and quantifying hand motor symptoms in clinical practice.