Portal veins of mice infected with Schistosoma mansoni exhibit an increased reactivity to 5-hydroxytryptamine

In chronic severe infection with Schistosoma mansoni, portal hypertension and related vascular alterations usually develop as a consequence of granulomatous response to eggs. In order to investigate a putative direct effect of worms on the reactivity of their host portal vein, mice infected only with male worms were used in the present study. An higher reactivity to 5-hydroxytryptamine (5-HT) characterized by an increase in the maximal contraction and sensitivity was observed in portal vein from infected mice compared to healthy mice. Blockade of NO-synthase with l-NAME induced a small increase in 5-HT potency in portal vein from non-infected mice without changing the amplitude of the contractions, whereas it did not alter the reactivity of veins from infected mice. The present results show that unisexual infection of mice with male S. mansoni increased the reactivity of the portal vein to 5-HT which seems to be partially related to an alteration in the nitric oxide release by endothelium.

Prolonged antiretroviral therapy initiated at seroconversion is associated with a polyfunctional HIV-1-specific T-cell profile comparable to that of long-term non-progressors (LTNPs)

Background: Early initiation of antiretroviral therapy (ART) may dramatically curtail cumulative immunological damage allowing maximal levels of immune preservation/reconstitution and induce an immunovirological status similar to that of HIV-1 LTNPs with low viral reservoirs and polyfunctional HIV-1 specific T cell responses.Methods: We performed a cross-sectional study of an HIV-1 seroconverter cohort on long-term ART (LTTS) and compared it to one of LTNPs. Inclusion criteria for 20 LTTS were: (a) ?4 years ART; (b) long-term aviremia and (c) absence of treatment failure and for 15 LTNPs: (a) ?7 years of documented HIV-1 infection; (b) <1000 HIV-1 RNA copies/mL and ?500 CD4+ T-cells/mm3 in >90% of measurements; (d) absence of AIDS-defining conditions; (e) ART-naı¨ve except for temporary ART for prevention of MTCT. In both cohorts, we analysed residual viral replication and reservoirs in peripheral blood, as measured by cellassociated HIV-1 RNA and DNA in PBMCs, respectively and used polychromatic flow cytometry to analyse HIV-1-specific CD4+ and CD8+ T-cell functional profile in terms of cytokine production using IFN-c, IL-2, TNF-a production.Results: Cell-associated DNA [47.7 (4.8-583.2) in LTTS and 19.7 (0.5-295.5) in LTNPS, p=0.10], and RNA [3.9 (0-36) and 5.8 (0-10.3), respectively] were shown to be similarly low in both cohorts. We identified 103 CD8 T cell epitope-specific responses, all subjects responding to ?1 epitope. Mean responding number of responding epitopes per patient was 2 and 4 in LTTS and LTNPS, respectively. Mean% of cytokine-secreting CD8 T cells was 0.37% and 0.50% (p=0.06), of these 43% and 39% (p=0.12) were secreting simultaneously IFN-c, IL-2 and TNF-a. Respective values for CD4 T cells were 0.28% and 0.33% (p=0.28) of which 33% and 30% (0.32) were secreting these 3 cytokines simultaneously.Conclusions: Long-term aviremia after very early ART initiation is associated with low levels of reservoirs saturation ad residual replication. Although less broad CD8 T cell responses were found in LTTS, HIV-1 specific CD4 and CD8 T cell responses showed similar magnitude and functional profile in the 2 cohorts. Our results indicate that prolonged ART initiated at the time of HIV-1 seroconversion is associated with immuno-virological features which resemble those of LTNPs. (BHIVA Research Award Winner 2008: Anna Garcia-Diaz.)

Hyperoxemia in newborn infants: detection by pulse oximetry.

Pulse oximetry has been proposed as a noninvasive continuous method for transcutaneous monitoring of arterial oxygen saturation of hemoglobin (tcSO2) in the newborn infant. The reliability of this technique in detecting hyperoxemia is controversial, because small changes in saturation greater than 90% are associated with relatively large changes in arterial oxygen tension (PaO2). The purpose of this study was to assess the reliability of pulse oximetry using an alarm limit of 95% tcSO2 in detecting hyperoxemia (defined as PaO2 greater than 90 mm Hg) and to examine the effect of varying the alarm limit on reliability. Two types of pulse oximeter were studied alternately in 50 newborn infants who were mechanically ventilated with indwelling arterial lines. Three arterial blood samples were drawn from every infant during routine increase of inspired oxygen before intratracheal suction, and PaO2 was compared with tcSO2. The Nellcor N-100 pulse oximeter identified all 26 hyperoxemic instances correctly (sensitivity 100%) and alarmed falsely in 25 of 49 nonhyperoxemic instances (specificity 49%). The Ohmeda Biox 3700 pulse oximeter detected 13 of 35 hyperoxemic instances (sensitivity 37%) and alarmed falsely in 7 of 40 nonhyperoxemic instances (specificity 83%). The optimal alarm limit, defined as a sensitivity of 95% or more associated with maximal specificity, was determined for Nellcor N-100 at 96% tcSO2 (specificity 38%) and for Ohmeda Biox 3700 at 89% tcSO2 (specificity 52%). It was concluded that pulse oximeters can be highly sensitive in detecting hyperoxemia provided that type-specific alarm limits are set and a low specificity is accepted.

Intraobserver and interobserver variability of ascending aorta diameter as assessed with ECG-gated MDCT: automatic versus manual measurements

Purpose: Recently morphometric measurements of the ascending aorta have been done with ECG-gated MDCT to help the development of future endovascular therapies (TCT) [1]. However, the variability of these measurements remains unknown. It will be interesting to know the impact of CAD (computer aided diagnosis) with automated segmentation of the vessel and automatic measurements of diameter on the management of ascending aorta aneurysms. Methods and Materials: Thirty patients referred for ECG-gated CT thoracic angiography (64-row CT scanner) were evaluated. Measurements of the maximum and minimum ascending aorta diameters were obtained automatically with a commercially available CAD and semi-manually by two observers separately. The CAD algorithms segment the iv-enhanced lumen of the ascending aorta into perpendicular planes along the centreline. The CAD then determines the largest and the smallest diameters. Both observers repeated the automatic measurements and the semimanual measurements during a different session at least one month after the first measurements. The Bland and Altman method was used to study the inter/intraobserver variability. A Wilcoxon signed-rank test was also used to analyse differences between observers. Results: Interobserver variability for semi-manual measurements between the first and second observers was between 1.2 to 1.0 mm for maximal and minimal diameter, respectively. Intraobserver variability of each observer ranged from 0.8 to 1.2 mm, the lowest variability being produced by the more experienced observer. CAD variability could be as low as 0.3 mm, showing that it can perform better than human observers. However, when used in nonoptimal conditions (streak artefacts from contrast in the superior vena cava or weak lumen enhancement), CAD has a variability that can be as high as 0.9 mm, reaching variability of semi-manual measurements. Furthermore, there were significant differences between both observers for maximal and minimal diameter measurements (p<0.001). There was also a significant difference between the first observer and CAD for maximal diameter measurements with the former underestimating the diameter compared to the latter (p<0.001). As for minimal diameters, they were higher when measured by the second observer than when measured by CAD (p<0.001). Neither the difference of mean minimal diameter between the first observer and CAD nor the difference of mean maximal diameter between the second observer and CAD was significant (p=0.20 and 0.06, respectively). Conclusion: CAD algorithms can lessen the variability of diameter measurements in the follow-up of ascending aorta aneurysms. Nevertheless, in non-optimal conditions, it may be necessary to correct manually the measurements. Improvements of the algorithms will help to avoid such a situation.

Some solutions to obtain very efficient separations in isocratic and gradient modes using small particles size and ultra-high pressure.

The UHPLC strategy which combines sub-2 microm porous particles and ultra-high pressure (>1000 bar) was investigated considering very high resolution criteria in both isocratic and gradient modes, with mobile phase temperatures between 30 and 90 degrees C. In isocratic mode, experimental conditions to reach the maximal efficiency were determined using the kinetic plot representation for DeltaP(max)=1000 bar. It has been first confirmed that the molecular weight of the compounds (MW) was a critical parameter which should be considered in the construction of such curves. With a MW around 1000 g mol(-1), efficiencies as high as 300,000 plates could be theoretically attained using UHPLC at 30 degrees C. By limiting the column length to 450 mm, the maximal plate count was around 100,000. In gradient mode, the longest column does not provide the maximal peak capacity for a given analysis time in UHPLC. This was attributed to the fact that peak capacity is not only related to the plate number but also to column dead time. Therefore, a compromise should be found and a 150 mm column should be preferentially selected for gradient lengths up to 60 min at 30 degrees C, while the columns coupled in series (3x 150 mm) were attractive only for t(grad)>250 min. Compared to 30 degrees C, peak capacities were increased by about 20-30% for a constant gradient length at 90 degrees C and gradient time decreased by 2-fold for an identical peak capacity.

Coronary Heart Disease Briefing

Coronary heart disease (CHD) is a collective term for diseases that occur when the walls of the coronary arteries become narrowed by a gradual build up of fatty material called atheroma. For the purpose of this briefing, CHD includes heart attack and angina (chest pain on exertion or stress). The Chronic Conditions Hub is a website that brings together information on chronic health conditions. It allows you to easily access, manage and share relevant information resources. The Chronic Conditions Hub includes the Institute of Public Health in Ireland’s (IPH) estimates and forecasts of the number of people living with chronic conditions. On the Chronic Conditions Hub you will find: - A Briefing for each condition - Detailed technical documentation - Detailed national and sub-national data that can be downloaded or explored using online data tools - A prevalence tool that allows you to calculate prevalence figures for your population data

Métabolisme énergétique des personnes âgées [Energy metabolism in the elderly].

The energy metabolism in elderly subjects is discussed on the basis of previous analyses of the influence of age on the three components of energy expenditure in man: basal metabolic rate, thermogenesis and physical activity. All three components are diminished in elderly people. We conclude that the modifications of body composition, in particular the age-related loss of lean body mass, result in decreased basal metabolic rate and probably also a blunted diet-induced thermogenesis. Moreover we emphasize that the decrease in physical activity observed in elderly people is the most likely causal factor.

On the function of proton-gated ion channels ASICs and TRPV1 : a patch-clamp study

AbstractAcidosis is encountered during tissue inflammation and triggers pain in humans. H+-gated ion channels are expressed at high levels in sensory neurons of the peripheral nervous system. Ion channels from two different families present the required pH sensitivity to detect the acidosis associated with peripheral inflammation: Acid-Sensing Ion Channels (ASICs) and the Transient Receptor Potential Vanilloid-1 (TRPV1) channel.ASICs are members of the Degenerin/Epithelial Na+ Channel family of ion channels. Six ASIC subunits have been identified in mammals (ASICla, -lb, -2a, -2b, -3 and -4). ASICs form In-activated voltage-insensitive homo- or heterotrimeric Na+ channels. TRPV1 is a member of the TRP family of ion channels and forms non-selective cation channels that mediate a sustained current. TRPV1 is activated by H+, heat (T>43°C), lipids, capsaicin, voltage and other stimuli. A stimulus can increase TRPV1 response to a different stimulus. For example H+ can shift the capsaicin concentration dependence of TRPV1 to lower values. ASICs and TRPV1 have been shown to be involved in inflammatory pain. Using the patch-clamp technique, we studied different aspects of the function of ASICs and TRPV1 in the physiological context of pain.In the first part of this thesis, we characterize the effect of a temperature increase from 25 to 35°C on the function of ASICs and TRPV1 in transfected CHO cells and primary cultures of rat DRG sensory neurons. ASICs give rise to transient currents while TRPV1 mediates a sustained current. In addition, ASICs and TRPV1 respond to H+ with distinct pH dependences. We assess the relative contribution of ASICs and TRPV1 to H+-evoked electrical signaling in rat DRG neurons and we conclude that ASICs are the most important pH sensors in the pH range 7.4 to 6.0 at 35°C in sensory neurons.ASICs and TRPV1 are expressed in the epithelium lining the lumen of the bladder (urothelium). The Bladder Pain Syndrome/Interstitial Cystitis (BPS/IC) is a painful condition associated with a dysfunction of the urothelial barrier and with inflammation. In the second part of this thesis, we show that human urothelial cells -the cell line TEU2 and primary cultures of human bladder urothelium- express functional ASICs but no functional TRPV1 channels. In addition, we show that the levels of ASIC2 and ASIC3 mRNA are increased in the urothelium of patients suffering from BPS/IC. These data suggest that ASICs are involved in the pathology of BPS/IC.Finally, we demonstrate that APETx2 inhibits the sensory neuron specific voltage-dependent Na+ channel Nav1.8. APETx2 was previously shown to inhibit homo- or heterotrimeric ASIC3- containing channels with IC5o from 0.08 to 1 μΜ. We show that APETx2 also inhibits Nav1.8 with an ICsoof «2.6 μΜ. APETx2 reduces the maximal conductance and induces a depolarizing shift in the voltage dependence of activation of Nav1.8. In current-clamp experiments, APETx2 reduces the number of action potentials (APs) evoked by a current ramp. Nav1.8 mediates most of the current during the AP upstroke and has been shown to be an important mediator of inflammatory pain. The fact that APETx2 inhibits two ion channels involved in inflammatory pain suggests that APETx2 or derivatives may represent novel analgesic compounds.RésuméL'acidose tissulaire est observée durant l'inflammation et entraine la douleur chez l'humain. Des canaux ioniques activés par les protons (H+) sont fortement exprimés dans les neurones sensoriels du système nerveux périphérique. De ceux-ci, les Acid-Sensing Ion Channels [ASICs) et Transient Receptor Potential Vanilloid-1 (TRPV1) présentent une sensibilité adéquate à l'acidité pour servir de détecteurs d'acidose.Les ASICs sont membres de la famille Degenerin/Epithelial Na* Channel. Six sous-unités ASIC ont été identifiées chez les mammifères (ASICla, -lb, -2a, -2b, -3 et -4). Les ASICs forment des canaux sélectifs au Na\ insensibles au voltage et activés par les H+. Les canaux fonctionnels sont des homo- ou hétérotrimères de sous-unités ASIC. TRPV1 est un membre de la famille TRP de canaux ioniques. Les canaux TRPV1 sont activés par les H+, la chaleur (T>43°Ç), les lipides, la capsaicine, le voltage et d'autres stimulus. L'activation de TRPV1 entraine un courant soutenu non-sélectif. Un stimulus peut augmenter la réponse de TRPV1 à un autre stimulus. Les H+ peuvent, par exemple, induire un décalage vers des valeurs plus faibles de la courbe de dépendance à la concentration de TRPV1 pour la capsaicine. Il a été démontré que les ASICs et TRPV1 sont impliqués dans la douleur inflammatoire. En utilisant la technique du patch-clamp, nous avons étudié différents aspects de la fonction des ASICs et de TRPV1 dans des contextes associés à la douleur.Dans la première partie de cette thèse, nous caractérisons l'effet d'une augmentation de température de 25 à 35°C sur la fonction des canaux ASICs et TRPV1, dans des cellules CHO transfectées et dans des cultures primaires de neurones sensoriels (DRG) de rat. L'activation des ASICs entraine l'apparition d'un courant transitoire tandis que l'activation de TRPV1 entraine un courant soutenu. De plus, les ASICs et TRPV1 possèdent des dépendances au pH différentes. Nous évaluons la contribution relative des ASICs et de TRPV1 au signalement électrique induit par les H+ et nous concluons que les ASICs sont les senseurs d'acidité les plus importants dans les neurones sensoriels, dans le domaine de pH de 7.4 à 6.0, à température corporelle.Les ASICs et TRPV1 sont exprimés dans l'épithélium recouvrant l'intérieur de la vessie (l'urothélium). Le Bladder Pain Syndrome/Interstitial Cystitis (BPS/IC) est une condition médicale douloureuse associée à une dysfonction de la barrière urothéliale et à une inflammation. Dans la seconde partie de cette thèse, nous démontrons que des cellules urothéliales (de la lignée cellulaire TEU2) et des cellules provenant de cultures primaires d'épithéliums de vessies humaines expriment des canaux ASIC fonctionnels mais pas de TRPV1 fonctionnels. De plus, nous montrons que le niveau d'expression de ASIC2 et -3 est augmenté dans l'urothélium de la vessie de patients souffrant de BPS/IC. Ces données suggèrent que les ASICs sont impliqués dans la pathologie BPS/IC.Pour finir, nous démontrons que la toxine APETx2 inhibe le canal spécifique aux neurones sensoriels Nav1.8, un membre de la famille des canaux sodiques dépendants du potentiel. Il a été démontré précédemment que la toxine APETx2 inhibe les canaux contenant une ou plusieurs sous-unités ASIC3 avec un ICso entre 0.08 et 1 μΜ. Nous montrons que la toxine APETx2 inhibe Nav1.8 avec un IC50 de «2.6 μΜ. La toxine APETx2 réduit la conductance maximale et induit un décalage de la dépendance au potentiel de Nav1.8 vers des valeurs plus positives. Dans des expériences de courant imposé sur des neurones sensoriels, la toxine APETx2 réduit le nombre de potentiels d'action induits par une rampe de courant. Nav1.8 est responsable de la majeure partie du courant durant la phase ascendante du potentiel d'action et a été démontré comme étant un médiateur important de la douleur inflammatoire. L'inhibition de deux types de canaux, impliqués dans la douleurs inflammatoire, par la toxine APETx2, suggère que cette dernière ou ses dérivés représentent des composés analgésiques prometteurs.

Reducing the learning curve for the treatment of morphoeic (sclerosing) basal cell carcinoma of the face.

The treatment of morphoeic (or sclerosing) basal cell carcinoma (mBCC) of the face is associated with high rates of incomplete excision and recurrence. A principal risk factor for incomplete resection is the grade of surgeon. We did a prospective, randomised study of 40 consecutive patients with mBCC of the face. The extent of the tumour was assessed under standard conditions by consultant surgeons and compared with assessments by resident surgeons with the help of the Varioscope, a combination of microscope and loupe glasses with strong illumination and a maximal magnification of 7x. The data from a former retrospective study of all excisions of mBCC of the face during a five-year period at the hospital served as control. Residents with the support of the Varioscope achieved a rate of incomplete excisions similar to that of consultants under standard conditions. There was a significant reduction of the rate of incomplete resections by resident surgeons thanks to high magnification and good lighting (p=0.02). High magnification and good lighting were useful in learning how to recognise skin changes associated with mBCC of the face and achieving a low rate of incomplete excisions.

Regulation of horizontal gene transfer of the catabolic island ICEclc

ICEclc is a mobile genetic element found in two copies on the chromosome of the bacterium Pseudomonas knackmussii B13. ICEclc harbors genes encoding metabolic pathways for the degradation of chlorocatechols (CLC) and 2-aminophenol (2AP). At low frequencies, ICEclc excises from the chromosome, closes into a circular DNA molecule which can transfer to another bacterium via conjugation. Once in the recipient cell, ICEclc can reintegrate into the chromosome by site-specific recombination. This thesis aimed at identifying the regulatory network underlying the decisions for ICEclc horizontal transfer (HGT). The first chapter is an introduction on integrative and conjugative elements (ICEs) more in general, of which ICEclc is one example. In particular I emphasized the current knowledge of regulation and conjugation machineries of the different classes of ICE. In the second chapter, I describe a transcriptional analysis using microarrays and other experiments to understand expression of ICEclc in exponential and stationary phase. By overlaying transcriptomic profiles with Northern hybridizations and RT- PCR data, we established a transcription map for the entire core region of ICEclc, a region assumed to encode the ICE conjugation process. We also demonstrated how transcription of the ICEclc core is maximal in stationary phase, which correlates to expression of reporter genes fused to key ICEclc promoters. In the third chapter, I present a transcriptome analysis of ICEclc in a variety of different host species, in order to explore whether there are species-specific differences. In the fourth chapter, I focus on the role of a curious ICEclc-encoded TetR-type transcriptional repressor. We find that this gene, which we name mfsR, not only controls its own expression but that of a set of genes for a putative multi-drug efflux pump (mfsABC) as well. By using a combination of biochemical and molecular biology techniques, I could show that MfsR specifically binds to operator boxes in two ICEclc promoters (PmfsR and PmfsA), inhibiting the transcription of both the mfsR and mfsABC-orf38184 operons. Although we could not detect a clear phenotype of an mfsABC deletion, we discuss the implications of pump gene reorganizations in ICEclc and close relatives. In the fifth chapter, we find that mfsR not only controls its own expression and that of the mfsABC operon, but is also indirectly controlling ICEclc transfer. Using gene deletions, microarrays, transfer assays and microscopy-based reporter fusions, we demonstrate that mfsR actually controls a small operon of three regulatory genes. The last gene of this mfsR operon, orf17162, encodes a LysR-type activator that when deleted strongly impairs ICEclc transfer. Interestingly, deletion of mfsR leads to transfer competence in almost all cells, thereby overruling the bistability process in the wild-type. In the final sixth chapter, I discuss the relevance of the present thesis and the resulting perspectives for future studies.

Changes in the vascular reactivity of the isolated tail arteries of spontaneous and renovascular hypertensive rats to endogenous and exogenous noradrenaline.

We have investigated the changes in the responses to noradrenaline of isolated tail arteries of spontaneously hypertensive (SHR) and renovascular hypertensive rats (Wistar-Kyoto: two-kidney, one-clip model, WKY:2K1C) compared with normotensive (Wistar-Kyoto, WKY) rats. Renovascular hypertension was induced by 4 weeks' unilateral renal artery clipping. Arteries were vasoconstricted with exogenous noradrenaline, electrical field stimulation or high potassium. The effects of the latter two stimuli were abolished by reserpine and so were presumably dependent on the presence of endogenous noradrenaline. In the SHR the maximal vasoconstriction produced by all three stimuli was greater than in WKY. Dose-response curves were steeper and there was no change in threshold. Vascular mass was greater. We interpret these results as showing an increase in vascular reactivity in the SHR caused by structural adaptation. The WKY:2K1C responses to noradrenaline could also be explained in terms of structural adaptation but there was no increase in vascular mass. Sensitivity to potassium and electrical stimulation was decreased, suggesting a defect in vascular neurotransmission. This was supported by the observations of a decreased arterial noradrenaline content and of decreased sensitivity to cocaine.

Rôle de l'inactivité physique dans l'étiologie de l'obésité [The role of physical inactivity in the etiology of obesity].

The activity-related energy expenditure mainly depends upon body weight, the type, intensity and duration of the exercise as well as the mechanical efficiency with which the subjects perform the work. Controversy still exist about the role of hypoactivity in the aetiology of obesity both in adolescence and adulthood. A number of experimental studies based on indirect assessment of physical activity (such as pedometers, accelerometers, cinematography and heart rate) have demonstrated a significant reduction in spontaneous physical activity in certain obese groups as compared to lean matched controls. On the other hand, direct measurements of energy expenditure (by indirect calorimetry) have shown a linear relationship between body weight and 24-hour (or activity-related) energy expenditure. It therefore appears that despite the greater placidity characterising some grossly obese subjects, the absolute rate of energy expenditure - particularly in weight bearing activities - is not lower than in lean subjects, since the hypoactivity does not fully compensate for the greater gross energy cost of a given activity.

Epidermal growth factor enhances the expression of an endogenous lectin in aggregating fetal brain cell cultures.

Aggregating cell cultures prepared from fetal rat telencephalon express the two subunits [cerebellar soluble lectins (CSL) 1 and 2] of a soluble, mannose-specific endogenous lectin (CSL) in a development-dependent manner. Increased CSL synthesis was found at an early postmitotic stage as well as during the period of maximal myelination. Repetitive treatment of early cultures with epidermal growth factor (EGF, 3nM) caused a great stimulation of CSL biosynthesis. Immunocytochemical studies revealed particularly intense CSL-specific staining in small, EGF-responsive cells, presumably glial cells. Large quantities of CSL-immunoreactive material were found also in the extracellular space and on the external side of the plasma membrane, indicating abundant release of CSL. The present findings suggest that EGF or EGF-related factors in the brain are able to regulate the expression of an endogenous lectin, affecting brain ontogeny.

Oxygen-sensing reporter strain of Pseudomonas fluorescens for monitoring the distribution of low-oxygen habitats in soil.

The root-colonizing bacterium Pseudomonas fluorescens CHA0 was used to construct an oxygen-responsive biosensor. An anaerobically inducible promoter of Pseudomonas aeruginosa, which depends on the FNR (fumarate and nitrate reductase regulation)-like transcriptional regulator ANR (anaerobic regulation of arginine deiminase and nitrate reductase pathways), was fused to the structural lacZ gene of Escherichia coli. By inserting the reporter fusion into the chromosomal attTn7 site of P. fluorescens CHA0 by using a mini-Tn7 transposon, the reporter strain, CHA900, was obtained. Grown in glutamate-yeast extract medium in an oxystat at defined oxygen levels, the biosensor CHA900 responded to a decrease in oxygen concentration from 210 x 10(2) Pa to 2 x 10(2) Pa of O(2) by a nearly 100-fold increase in beta-galactosidase activity. Half-maximal induction of the reporter occurred at about 5 x 10(2) Pa. This dose response closely resembles that found for E. coli promoters which are activated by the FNR protein. In a carbon-free buffer or in bulk soil, the biosensor CHA900 still responded to a decrease in oxygen concentration, although here induction was about 10 times lower and the low oxygen response was gradually lost within 3 days. Introduced into a barley-soil microcosm, the biosensor could report decreasing oxygen concentrations in the rhizosphere for a 6-day period. When the water content in the microcosm was raised from 60% to 85% of field capacity, expression of the reporter gene was elevated about twofold above a basal level after 2 days of incubation, suggesting that a water content of 85% caused mild anoxia. Increased compaction of the soil was shown to have a faster and more dramatic effect on the expression of the oxygen reporter than soil water content alone, indicating that factors other than the water-filled pore space influenced the oxygen status of the soil. These experiments illustrate the utility of the biosensor for detecting low oxygen concentrations in the rhizosphere and other soil habitats.