bluuebunny/crossref_metadata_2025 huggingface dataset:
Voluntary muscle and motor cortical activation during progressive exercise and passively induced hyperthermia
Authors: Périard Julien D. , Christian Ryan J. , Knez Wade L. , Racinais Sébastien
Published: September 2013

New findings

What is the central question of this study?

We examined whether passive hyperthermia exacerbates central fatigue due to an increase in peak muscle relaxation rate, and whether exercise‐induced hyperthermia attenuates this response because of a reduction in contractile speed related to peripheral fatigue.

What is the main finding and its importance?

Exercise and passive hyperthermia increase muscle relaxation rate. An increase from moderate to severe passive hyperthermia enhances this rate, but without exacerbating force loss or voluntary muscle and cortical activation, relative to exercise. The centrally mediated rate of activation appears sufficient to overcome the increase in peak muscle relaxation.

This study examined whether central fatigue was exacerbated by an increase in muscle contractile speed caused by passive hyperthermia (PaH) and whether exercise‐induced hyperthermia (ExH) combined with related peripheral fatigue influenced this response. The ExH was induced by cycling at 60% of maximal oxygen uptake in 38°C conditions and the PaH by sitting in a 48°C climate chamber. Ten men performed brief (∼5 s) and sustained (30 s) maximal voluntary isometric contractions (MVCs) of the knee extensors at baseline (CON, ∼37.1°C) and during moderate (MOD, ∼38.5°C) and severe (SEV, ∼39.5°C) hyperthermia. Motor nerve and transcranial magnetic stimulation were used to assess voluntary muscle and cortical activation level, along with contractile properties. Brief MVC force decreased to a similar extent during SEV‐ExH (−8%) and SEV‐PaH (−6%; P < 0.05 versus CON). Sustained MVC force also decreased during MOD‐ExH (−10%), SEV‐ExH (−13%) and SEV‐PaH (−7%; P < 0.01 versus CON). Motor nerve and cortical activation were reduced on reaching MOD (∼3%) and SEV (∼5%) ExH and PaH during the brief and sustained MVCs (P < 0.01 versus CON). Peak twitch force decreased on reaching SEV‐ExH and SEV‐PaH (P < 0.05 versus CON). Following transcranial magnetic stimulation, during the brief and sustained MVCs the peak muscle relaxation rate increased in ExH and PaH (P < 0.01 versus CON). The increase was greatest during the sustained contraction in SEV‐PaH (P < 0.01), but this did not exacerbate central fatigue relative to ExH. These results indicate that during fatiguing cycling exercise in the heat, quadriceps peak relaxation rate increases. However, the centrally mediated rate of activation appears sufficient to overcome even the largest increase in muscle relaxation rate, seen during SEV‐PaH.
Upregulation of a local renin–angiotensin system in the rat carotid body during chronic intermittent hypoxia
Authors: Lam Siu‐Yin , Liu Yu , Ng Kwong‐Man , Liong Emily C. , Tipoe George L. , Leung Po Sing , Fung Man‐Lung
Published: September 2013

New Findings

What is the central question of this study?

Expression of the renin–angiotensin system (RAS) may play a pathogenic role in the augmented activity of carotid body chemosensitive cells and the carotid body (CB) inflammation in chronic intermittent hypoxia (IH). The aim of this study was to examine the expression and function of the RAS components in the CB during chronic IH resembling a severe sleep‐apnoeic condition.

What is the main finding and its importance?

Chronic IH induces a functional upregulation of the RAS expression in the CB. The upregulation of RAS expression could play a pathogenic role in the augmented CB excitability during IH, which is relevant to early pathogenesis in sleep‐disordered breathing.

The carotid body (CB) plays an important role in the alteration of cardiorespiratory activity in chronic intermittent hypoxia (IH) associated with sleep‐disordered breathing, which may be mediated by local expression of the renin–angiotensin system (RAS). We hypothesized a pathogenic role for IH‐induced RAS expression in the CB. The CB expression of RAS components was examined in rats exposed to IH resembling a severe sleep‐apnoeic condition for 7 days. In situ hybridization showed an elevated expression of angiotensinogen in the CB glomus cells in the hypoxic group when compared with the normoxic control group. Immunohistochemical studies and Western blot analysis revealed increases in the protein level of both angiotensinogen and angiotensin II type 1 (AT1) receptors in the hypoxic group, which were localized to the glomic clusters containing tyrosine hydroxylase. RT‐PCR studies confirmed that levels of the mRNA expression of angiotensinogen, angiotensin‐converting enzyme, AT1a and AT2 receptors were significantly increased in the CBs of the hypoxic rats. Functionally, the [Ca2+]i response to exogenous angiotensin II was enhanced in fura‐2‐loaded glomus cells dissociated from hypoxic rats when compared with those of the normoxic control animals. Pretreatment with losartan, but not PD123319, abolished the angiotensin II‐induced [Ca2+]i response, suggesting an involvement of AT1 receptors. Moreover, daily treatment of the IH group of rats with losartan attenuated the levels of oxidative stress, gp91phox expression and macrophage infiltration in the CB. Collectively, the upregulated local RAS expression could play a pathogenic role in the augmented CB activity and local inflammation via AT1 receptor activation during IH conditions in patients with sleep‐disordered breathing.
The stimulating effect of ghrelin on gastric motility and firing activity of gastric‐distension‐sensitive hippocampal neurons and its underlying regulation by the hypothalamus
Authors: Xu Luo , Gong Yanling , Wang Hongbo , Sun Xiangrong , Guo Feifei , Gao Shengli , Gu Fang
Published: September 2013

New Findings

What is the central question of this study?

Is there a direct pathway of ghrelin from the hypothalamic arcuate nucleus to the hippocampus? Is this pathway involved in the regulation of gastric motility and gastric afferent signalling?

What is the main finding and its importance?

There exists a direct pathway of ghrelin from the hypothalamic arcuate nucleus to the hippocampus that is involved in the regulation of gastric motility. In the emotional hub hippocampus, ghrelin is involved in the regulation of gastric motility and gastric afferent signalling. These effects can be regulated by the hypothalamic arcuate nucleus. This supports and advances the theory of energy balance involving the regulation of the central and brain–gut peptides.

Ghrelin is an acylated peptide originally identified in the rat stomach as the endogenous ligand for growth hormone secretagogue receptor (GHSR) that promotes gastric motility. Our aims were to explore the effects of ghrelin on gastric‐distension‐sensitive neurons in the hippocampus and the potential for ghrelin to regulate gastric motility through the arcuate nucleus (Arc). Single‐unit discharges in the hippocampus were recorded extracellularly, and gastric motility in conscious rats was monitored. The expression of GHSR‐1a in the hippocampus was determined by PCR, Western blot and fluo‐immunohistochemistry staining. Retrograde tracing and fluo‐immunohistochemistry staining were used to determine ghrelin neuron projection. Ghrelin–Fluoro‐Gold double‐labelled neurons and GHSR‐1a expression were observed in the Arc and hippocampus, respectively. There were gastric‐distension‐sensitive neurons in the hippocampus that could be excited by ghrelin or by electrical stimulation of the Arc. The excitatory effects could be blocked completely or partly by pretreatment with the ghrelin receptor antagonist [d‐Lys‐3]‐GHRP‐6. Gastric motility was significantly promoted by the administration of ghrelin into the hippocampus in a dose‐dependent manner that could be completely abolished by [d‐Lys‐3]‐GHRP‐6. Electrical stimulation of the Arc could promote gastric motility as well. Nevertheless, these effects could be mitigated by pretreatment with [d‐Lys‐3]‐GHRP‐6. Electrical lesioning of the hippocampus diminished the excitatory effects on gastric motility that were induced by electrical stimulation the Arc. Our findings suggest that ghrelin plays an important role in promoting gastric motility via the hippocampus. The Arc may be involved in regulation of the influence of the hippocampus on gastric motility.
The influence of gap junction network complexity on pulmonary artery smooth muscle reactivity in normoxic and chronically hypoxic conditions
Authors: Gosak Marko , Guibert Christelle , Billaud Marie , Roux Etienne , Marhl Marko
Published: September 2013

New Findings

What is the central question of this study?

Experimental results on intrapulmonary arteries indicate that the relationship between gap junctional intercellular communication and its functional involvement in tissue reactivity is very complex, both in normoxic and in chronically hypoxic conditions. The relationship between the gap junction network and vasoreactivity is poorly known and needs to be explored, including theoretical modelling approaches.

What is the main finding and its importance?

Our results indicate that the role of gap junctions and their contribution to intrapulmonary artery reactivity depends crucially on the topology of the gap junctional communication network. In normoxia, myocytes are connected in a complex network, whereas chronic hypoxia is related to loss of the network complexity, leading to hypersensitivity.

Experiments on intrapulmonary arteries (IPAs) isolated from rats maintained in normoxia and chronic hypobaric hypoxia showed that in normoxia, the IPA contractile sensitivity to KCl was not modified by gap junction inhibition. In contrast, chronic hypoxia induced an endothelium‐independent hypersensitivity, which was suppressed by gap junction inhibition. For the theoretical analysis of these results, we developed a model of interconnected myocytes. Given that smooth muscle cells in IPAs are known to communicate via gap junctions, we regard the cytoarchitecture of the IPA as a spatial network, in which nodes represent individual smooth muscle cells and the links signify intercellular communication. A single‐cell model that drives the dynamics of individual nodes includes the major elements of voltage‐dependent Ca2+ signalling. In addition, interindividual variability of SMCs is introduced by distributing the reversal potentials for K+. Cell‐to‐cell connection consists of passive Ca2+ diffusion and electrical coupling, and connection between cells is determined by the topology of the intercellular network. Model predictions indicate that the experimental results can be explained by topological modifications and not by changes in the number of gap junctions. According to the model, in normoxia the myocytes are connected in a complex network, whereas chronic hypoxia is related to loss of complexity, leading to hypersensitivity. Our results thus indicate that chronic hypoxia entails gap junction network rearrangements, leading to disturbances in the intercellular communication pathways.
The cardiovascular actions of fractalkine/CX3CL1 in the hypothalamic paraventricular nucleus are attenuated in rats with heart failure
Authors: Ruchaya P. J. , Antunes V. R. , Paton J. F. R. , Murphy D. , Yao S. T.
Published: September 2013

New Findings

What is the central question of this study?

The chemokine fractalkine (FKN) and its cognate receptor, CX3CR1, are expressed in the brain, but their distribution and function within the paraventricular nucleus of the hypothalamus (PVN) have not been previously investigated.

What is the main finding and its importance?

We show that both FKN and CX3CR1 receptor mRNA and protein are expressed in the PVN and that FKN elicits hypotension and tachycardia when exogeneously applied by microinjection, an effect that is attenuated in rats with heart failure. These findings are important because they demonstrate that FKN and its cognate receptor are expressed and play a role in controlling cardiovascular function within the PVN.

The paraventricular nucleus (PVN) of the hypothalamus plays an important role in the regulation of sympathetic nerve activity, which is significantly elevated in chronic heart failure (CHF). Fractalkine (FKN) and its cognate receptor, CX3CR1, are constitutively expressed in the central nervous system, but their role and physiological significance are not well known. The aims of the present study were to determine whether FKN plays a cardiovascular role within the PVN and to investigate how the actions of FKN might be altered in CHF. We show that both FKN and CX3CR1 are expressed on neurons in the PVN of rats, suggesting that they may have a physiological function in this brain nucleus. Unilateral microinjection of FKN directly into the PVN of anaesthetized rats elicited a significant dose‐related decrease in blood pressure (1.0 nmol, −5 ± 3 mmHg; 2.5 nmol, −13 ± 2 mmHg; 5.0 nmol, −22 ± 3 mmHg; and 7.5 nmol, −32 ± 3 mmHg) and a concomitant increase in heart rate (1.0 nmol, 6 ± 3 beats min−1; 2.5 nmol, 11 ± 3 beats min−1; 5 nmol, 18 ± 4 beats min−1; and 7.5 nmol, 27 ± 5 beats min−1) compared with control saline microinjections. In order to determine whether FKN signalling is altered in rats with CHF, we first performed quantitative RT‐PCR and Western blot analysis and followed these experiments with functional studies in rats with CHF and sham‐operated control rats. We found a significant increase in CX3CR1 mRNA and protein expression, as determined by quantitative RT‐PCR and Western blot analysis, respectively, in the PVN of rats with CHF compared with sham‐operated control rats. We also found that the blood pressure effects of FKN (2.5 nmol in 50 nl) were significantly attenuated in rats with CHF (change in mean arterial pressure, −6 ± 3 mmHg) compared with sham‐operated control rats (change in mean arterial pressure, −16 ± 6 mmHg). These data suggest that FKN and its receptor, CX3CR1, modulate cardiovascular function at the level of the PVN and that the actions of FKN within this nucleus are altered in heart failure.
Exercise reveals impairments in left ventricular systolic function in patients with metabolic syndrome
Authors: Fournier Sara B. , Reger Brian L. , Donley David A. , Bonner Daniel E. , Warden Bradford E. , Gharib Wissam , Failinger Conard F. , Olfert Melissa D. , Frisbee Jefferson C. , Olfert I. Mark , Chantler Paul D.
Published: September 2013

New Findings

What is the central question of this study?

Metabolic syndrome (MetS) is associated with a threefold increase in risk of cardiovascular disease mortality, which may be mediated, in part, by impaired left ventricular systolic function. The severity of left ventricular and arterial dysfunction during dynamic exercise in individuals with MetS without diabetes and/or overt cardiovascular disease has not previously been explored.

What is the main finding and its importance?

Cardiovascular function was characterized at rest and during peak exercise using echocardiography and gas exchange. During exercise, individuals with MetS displayed impaired left ventricular contractility, a blunted arterial–ventricular coupling reserve and limited aerobic capacity. These findings provide insight into the pathophysiological changes that may occur to predispose individuals with MetS to an increased risk of cardiovascular disease.

Metabolic syndrome (MetS) is the manifestation of a cluster of cardiovascular risk factors and is associated with a threefold increase in the risk of cardiovascular morbidity and mortality, which is suggested to be mediated, in part, by resting left ventricular (LV) systolic dysfunction. However, to what extent resting LV systolic function is impaired in MetS is controversial, and there are no data indicating whether LV systolic function is impaired during exercise. Accordingly, the objective of this study was to examine comprehensively the LV and arterial responses to exercise in individuals with MetS without diabetes and/or overt cardiovascular disease in comparison to a healthy control population. Cardiovascular function was characterized using Doppler echocardiography and gas exchange in individuals with MetS (n= 27) versus healthy control subjects (n= 20) at rest and during peak exercise. At rest, individuals with MetS displayed normal LV systolic function but reduced LV diastolic function compared with healthy control subjects. During peak exercise, individuals with MetS had impaired contractility, pump performance and vasodilator reserve capacity versus control subjects. A blunted contractile reserve response resulted in diminished arterial–ventricular coupling reserve and limited aerobic capacity in individuals with MetS versus control subjects. These findings are of clinical importance, because they provide insight into the pathophysiological changes in MetS that may predispose this population of individuals to an increased risk of cardiovascular morbidity and mortality.
Experimentally Observed Unsteady Work at Inlet to and Exit From an Axial Flow Turbine Rotor
Authors: Rose Martin G. , Jenny Philipp , Gier Jochen , Abhari Reza S.
Published: September 2013

World literature has introduced the aerodynamic importance of unsteadiness in turbines. In particular, the unsteady static pressure field determines the work of the machine. The unsteadiness can redistribute the total pressure in a cascade with wake interaction. It has been shown that differences in work between wake and free stream can act to rectify the wakes and boost efficiency. In this paper, fast response aerodynamic probe (FRAP) data are used to study the nature of the unsteady work in the flow at entry to and exit from a rotating turbine blade. The topic is addressed experimentally, theoretically, and computationally. It is found at both rotor inlet and exit that upstream wakes influence the unsteady work distribution. The relationship between the unsteady work in the absolute frame, the relative frame, and the momentum of the fluid circumferentially is derived and verified experimentally. Computational results (unsteady Reynolds-averaged Navier–Stokes (URANS)) are compared to the experimental results: reasonable agreement is found at rotor exit, but significant differences at rotor inlet are found. The computational fluid dynamics (CFD) has failed to capture the von Karman vortices and has dramatically lower levels of unsteady work. The experimental unsteady work distribution suggests possible effects of wake bending and vortex instability.
Economic Potential of Innovative Receiver Concepts With Different Solar Field Configurations for Supercritical Steam Cycles
Authors: Singer Csaba , Buck Reiner , Pitz-Paal Robert , Müller-Steinhagen Hans
Published: September 2013

The cost reduction potential of solar power towers (SPT) is an important issue concerning its market introduction. Raising the steam process temperature and pressure can lead to a cost reduction due to increased overall plant efficiency. Thus, for new receiver configurations, a supercritical steam cycle operated at 300 bar/600 °C/610 °C live steam conditions was assumed. The considered systems include innovative direct absorption receivers, either with conventional or beam down heliostat field layouts. For the beam down option, the receiver is assumed to be a cylindrical vessel with a flow-through porous absorber structure at the internal lateral area of the cylinder. The direct absorption receiver option consists of a cylindrical barrel with downwards oriented aperture, whose absorber structure at the internal lateral area is cooled by a molten salt film. For the assessment, CFD based methods are developed and able to examine the receiver efficiency characteristics. Based on the receiver thermal efficiency characteristics and the solar field characteristics, the annual performance is evaluated using hourly time series. The assessment methodology is based on the European Concentrated Solar Thermal Roadmap (ECOSTAR) study and enables the prediction of the annual performance and the levelized cost of electricity (LCOE). Applying appropriate cost assumptions from literature, the LCOE are estimated for each considered SPT concept and compared to tubular receiver concepts with molten salt and liquid metal cooling. The power level of the compared concepts and the reference case is 200 MWel. The sensitivity of the specific cost assumptions is analyzed. No detailed evaluation is done for the thermal storage, but comparable storage utilization and costs are assumed for all cases. At optimized plant parameters, the results indicate a LCOE reduction potential of up to 0.5% for beam down and of up to 7.2% for the direct absorption receiver compared to today's state of the art molten salt solar tower technology.
Computational Analysis of a Pipe Flow Distributor for a Thermocline Based Thermal Energy Storage System
Authors: Afrin Samia , Kumar Vinod , Bharathan Desikan , Glatzmaier Greg C. , Ma Zhiwen
Published: September 2013

The overall efficiency of a concentrating solar power (CSP) plant depends on the effectiveness of thermal energy storage (TES) system (Kearney and Herrmann, 2002, “Assessment of a Molten Salt Heat Transfer Fluid,” ASME). A single tank TES system consists of a thermocline region which produces the temperature gradient between hot and cold storage fluid by density difference (Energy Efficiency and Renewable Energy, http://www.eere.energy.gov/basics/renewable_energy/thermal_storage.html). Preservation of this thermocline region in the tank during charging and discharging cycles depends on the uniformity of the velocity profile at any horizontal plane. Our objective is to maximize the uniformity of the velocity distribution using a pipe-network distributor by varying the number of holes, distance between the holes, position of the holes and number of distributor pipes. For simplicity, we consider that the diameter of the inlet, main pipe, the distributor pipes and the height and the width of the tank are constant. We use Hitec® molten salt as the storage medium and the commercial software Gambit 2.4.6 and Fluent 6.3 for the computational analysis. We analyze the standard deviation in the velocity field and compare the deviations at different positions of the tank height for different configurations. Since the distance of the holes from the inlet and their respective arrangements affects the flow distribution throughout the tank; we investigate the impacts of rearranging the holes position on flow distribution. Impact of the number of holes and distributor pipes are also analyzed. We analyze our findings to determine a configuration for the best case scenario.
Drag Reduction Using Riblet Film Applied to Airfoils for Wind Turbines
Authors: Sareen Agrim , Deters Robert W. , Henry Steven P. , Selig Michael S.
Published: September 2013

This paper presents results of a study that was commissioned by the 3M Renewable Energy Division to measure the drag reduction by using riblet film on airfoils specifically designed for wind turbine applications. The DU 96-W-180 airfoil was tested with four different symmetrical V-shaped riblet sizes (44, 62, 100, and 150-μm) at three Reynolds numbers (1 × 106, 1.5 × 106, and 1.85 × 106) and at angles of attack spanning the low drag range of the airfoil. Tests were run with riblet film covering different sections of the airfoil in order to determine the optimal riblet location in terms of drag reduction. Results showed that the magnitude of drag reduction depended on the angle of attack, Reynolds number, riblet size, and riblet location. For some configurations, riblets produced significant drag reduction of up to 5%, while for others riblets were detrimental. Trends in the results indicated an optimum riblet size of 62-μm for the range of Reynolds numbers at which tests were conducted. The airfoil chord was 18 in (0.457 m). Results also showed that each riblet size performed best at a given Reynolds number with the optimal Reynolds number decreasing with an increase in riblet size.
Numerical Investigation of Water and Temperature Distributions for Open-Cathode Polymer Electrolyte Fuel Cell Stack With Edge Cooling
Authors: Sasmito Agus P. , Shamim Tariq , Birgersson Erik , Mujumdar Arun S.
Published: September 2013

Portable and motive applications of open-cathode polymer electrolyte fuel cells (PEFCs) require not only good stack performance but also a light and compact design. In this context, we explore how edge cooling with three different fin designs—one standard rectangular fin and two triangular fins that essentially halve the size of the fins—can improve the thermal and water envelopes inside the stack as well as stack performance while reducing the overall volume. The results suggest that all three edge-cooling designs give rise to lower and more uniform local temperature distributions as well as higher and more uniform hydration levels at the membrane in the stack compared to the conventional open-cathode PEFC without fins and design with additional air coolant plates. In addition, edge cooling design with one of the triangular fins yields the best performance (around 5% higher in term of power per unit catalyst area and power per unit weight as well as ∼10% higher in term of power per unit volume as compared to other designs). Overall, the triangular fin design shows potential to be used in, for example, automotive applications due to its high performance as well as lightweight and compact design.
Distinguishable Epidemics of Multidrug-Resistant
Salmonella
Typhimurium DT104 in Different Hosts
Authors: Mather A. E. , Reid S. W. J. , Maskell D. J. , Parkhill J. , Fookes M. C. , Harris S. R. , Brown D. J. , Coia J. E. , Mulvey M. R. , Gilmour M. W. , Petrovska L. , de Pinna E. , Kuroda M. , Akiba M. , Izumiya H. , Connor T. R. , Suchard M. A. , Lemey P. , Mellor D. J. , Haydon D. T. , Thomson N. R.
Published: September 2013

Sourcing Antibiotic Resistance

It is widely assumed that antibiotic resistance in farm animals contributes in a major way to antibiotic resistance in humans.

Mather
et al.

(p.
1514
, published online 12 September; see the Perspective by

Woolhouse and Ward
)

analyzed hundreds of genome sequences from
Salmonella
isolates collected from both livestock and patients in Scotland between 1990 and 2004. The relative contributions of animal-derived and human-derived sources of infection were quantified and the phylogenetic diversity of resistance profiles was matched with bacterial phylogenies. The results suggest that most human infections are caught from other humans rather than from livestock and that humans harbor a greater diversity of antibiotic resistance.
Aspergillus fumigatus SidJ Mediates Intracellular Siderophore Hydrolysis
Authors: Gründlinger Mario , Gsaller Fabio , Schrettl Markus , Lindner Herbert , Haas Hubertus
Published: September 2013

Siderophore-mediated iron handling is crucial for the virulence of
Aspergillus fumigatus
. Here we identified a new component of its siderophore metabolism, termed SidJ, which is encoded by AFUA_3G03390. The encoding gene is localized in a siderophore biosynthetic gene cluster that is conserved in a variety of fungi. During iron starvation, SidJ deficiency resulted in decreased growth and increased intracellular accumulation of hydrolysis products of the siderophore fusarinine C. The implied role in siderophore hydrolysis is consistent with a putative esterase domain in SidJ, which now represents the first functionally characterized member of the DUF1749 (
d
omain of
u
nknown
f
unction) protein family, with members found exclusively in fungi and plants.
Bacterial Contribution to Dissolved Organic Matter in Eutrophic Lake Kasumigaura, Japan
Authors: Kawasaki Nobuyuki , Komatsu Kazuhiro , Kohzu Ayato , Tomioka Noriko , Shinohara Ryuichiro , Satou Takayuki , Watanabe Fumiko Nara , Tada Yuya , Hamasaki Koji , Kushairi M. R. M. , Imai Akio
Published: September 2013

Incubation experiments using filtered waters from Lake Kasumigaura were conducted to examine bacterial contribution to a dissolved organic carbon (DOC) pool. Bacterial abundance, bacterial production, concentrations of DOC, total dissolved amino acids (TDAA), and total dissolved neutral sugars (TDNS) were monitored during the experiments. Bacterial production during the first few days was very high (20 to 35 μg C liter−1day−1), accounting for 40 to 70% of primary production. The total bacterial production accounted for 34 to 55% of the DOC loss during the experiment, indicating high bacterial activities in Lake Kasumigaura. The DOC degradation was only 12 to 15%, whereas the degradation of TDAA and TDNS ranged from 30 to 50%, suggesting the preferential usage of TDAA and TDNS. The contribution of bacterially derived carbon to a DOC pool in Lake Kasumigaura was estimated usingd-amino acids as bacterial biomarkers and accounted for 30 to 50% of the lake DOC. These values were much higher than those estimated for the open ocean (20 to 30%). The ratio of bacterially derived carbon to bulk carbon increased slightly with time, suggesting that the bacterially derived carbon is more resistant to microbial degradation than bulk carbon. This is the first study to estimate the bacterial contribution to a DOC pool in freshwater environments. These results indicate that bacteria play even more important roles in carbon cycles in freshwater environments than in open oceans and also suggests that recent increases in recalcitrant DOC in various lakes could be attributed to bacterially derived carbon. The potential differences in bacterial contributions to dissolved organic matter (DOM) between freshwater and marine environments are discussed.
Analysis of Genes for Succinoyl Trehalose Lipid Production and Increasing Production in Rhodococcus sp. Strain SD-74
Authors: Inaba Tomohiro , Tokumoto Yuta , Miyazaki Yusuke , Inoue Naoyuki , Maseda Hideaki , Nakajima-Kambe Toshiaki , Uchiyama Hiroo , Nomura Nobuhiko
Published: September 2013

Succinoyl trehalose lipids (STLs) are promising glycolipid biosurfactants produced from
n
-alkanes that are secreted by
Rhodococcus
species bacteria. These compounds not only exhibit unique interfacial properties but also demonstrate versatile biochemical actions. In this study, three novel types of genes involved in the biosynthesis of STLs, including a putative acyl coenzyme A (acyl-CoA) transferase (
tlsA
), fructose-bisphosphate aldolase (
fda
), and alkane monooxygenase (
alkB
), were identified. The predicted functions of these genes indicate that alkane metabolism, sugar synthesis, and the addition of acyl groups are important for the biosynthesis of STLs. Based on these results, we propose a biosynthesis pathway for STLs from alkanes in
Rhodococcus
sp. strain SD-74. By overexpressing
tlsA
, we achieved a 2-fold increase in the production of STLs. This study advances our understanding of bacterial glycolipid production in
Rhodococcus
species.
Role of Filamentous Phage SW1 in Regulating the Lateral Flagella of Shewanella piezotolerans Strain WP3 at Low Temperatures
Authors: Jian Huahua , Xiao Xiang , Wang Fengping
Published: September 2013

Low-temperature ecosystems represent the largest biosphere on Earth, and yet our understanding of the roles of bacteriophages in these systems is limited. Here, the influence of the cold-active filamentous phage SW1 on the phenotype and gene transcription of its host,
Shewanella piezotolerans
WP3 (WP3), was investigated by construction of a phage-free strain (WP3ΔSW1), which was compared with the wild-type strain. The expression of 49 genes, including 16 lateral flagellar genes, was found to be significantly influenced by SW1 at 4°C, as demonstrated by comparative whole-genome microarray analysis. WP3ΔSW1 was shown to have a higher production of lateral flagella than WP3 and enhanced swarming motility when cultivated on solid agar plates. Besides, SW1 has a remarkable impact on the expression of a variety of host genes in liquid culture, particularly the genes related to the membrane and to the production of lateral flagella. These results suggest that the deep-sea bacterium WP3 might balance the high-energy demands of phage maintenance and swarming motility at low temperatures. The phage SW1 is shown to have a significant influence on the swarming ability of the host and thus may play an important role in adjusting the fitness of the cells in the deep-sea environment.
Single-Cell Measurements of Enzyme Levels as a Predictive Tool for Cellular Fates during Organic Acid Production
Authors: Zdraljevic Stefan , Wagner Drew , Cheng Kevin , Ruohonen Laura , Jäntti Jussi , Penttilä Merja , Resnekov Orna , Pesce C. Gustavo
Published: September 2013

Organic acids derived from engineered microbes can replace fossil-derived chemicals in many applications. Fungal hosts are preferred for organic acid production because they tolerate lignocellulosic hydrolysates and low pH, allowing economic production and recovery of the free acid. However, cell death caused by cytosolic acidification constrains productivity. Cytosolic acidification affects cells asynchronously, suggesting that there is an underlying cell-to-cell heterogeneity in acid productivity and/or in resistance to toxicity. We used fluorescence microscopy to investigate the relationship between enzyme concentration, cytosolic pH, and viability at the single-cell level in
Saccharomyces cerevisiae
engineered to synthesize xylonic acid. We found that cultures producing xylonic acid accumulate cells with cytosolic pH below 5 (referred to here as “acidified”). Using live-cell time courses, we found that the probability of acidification was related to the initial levels of xylose dehydrogenase and sharply increased from 0.2 to 0.8 with just a 60% increase in enzyme abundance (Hill coefficient, >6). This “switch-like” relationship likely results from an enzyme level threshold above which the produced acid overwhelms the cell's pH buffering capacity. Consistent with this hypothesis, we showed that expression of xylose dehydrogenase from a chromosomal locus yields ∼20 times fewer acidified cells and ∼2-fold more xylonic acid relative to expression of the enzyme from a plasmid with variable copy number. These results suggest that strategies that further reduce cell-to-cell heterogeneity in enzyme levels could result in additional gains in xylonic acid productivity. Our results demonstrate a generalizable approach that takes advantage of the cell-to-cell variation of a clonal population to uncover causal relationships in the toxicity of engineered pathways.
Prevalence of Viral Photosynthetic and Capsid Protein Genes from Cyanophages in Two Large and Deep Perialpine Lakes
Authors: Zhong Xu , Jacquet Stéphan
Published: September 2013

Cyanophages are important components of aquatic ecosystems, but their genetic diversity has been little investigated in freshwaters. A yearlong survey was conducted in surface waters of the two largest natural perialpine lakes in France (Lake Annecy and Lake Bourget) to investigate part of this cyanophage diversity through the analysis of both structural (e.g.,
g20
) and functional (e.g.,
psbA
) genes. We found that these cyanophage signature genes were prevalent throughout the year but that the community compositions of
g20
cyanomyoviruses were significantly different between the two lakes. In contrast,
psbA
-containing cyanophages seemed to be more similar between the two ecosystems. We also found that a large proportion of
g20
sequences grouped with cyanomyophage isolates.
psbA
sequences, belonging to phages of
Synechococcus
spp., were characterized by distinct triplet motifs (with a novel viral triplet motif, EFE). Thus, our results show that cyanophages (i) are a diverse viral community in alpine lakes and (ii) are clearly distinct from some other freshwater and marine environments, suggesting the influence of unique biogeographic factors.
Enhanced Biotransformation of Fluoranthene by Intertidally Derived Cunninghamella elegans under Biofilm-Based and Niche-Mimicking Conditions
Authors: Mitra Sayani , Pramanik Arnab , Banerjee Srijoni , Haldar Saubhik , Gachhui Ratan , Mukherjee Joydeep
Published: September 2013

The aims of the investigation were to ascertain if surface attachment of
Cunninghamella elegans
and niche intertidal conditions provided in a bioreactor influenced biotransformation of fluoranthene by
C. elegans
. A newly designed polymethylmethacrylate (PMMA) conico-cylindrical flask (CCF) holding eight equidistantly spaced rectangular strips mounted radially on a circular disc allowed comparison of fluoranthene biotransformation between CCFs with a hydrophobic surface (PMMA-CCF) and a hydrophilic glass surface (GS-CCF) and a 500-ml Erlenmeyer flask (EF). Fluoranthene biotransformation was higher by 22-fold, biofilm growth was higher by 3-fold, and cytochrome P450 gene expression was higher by 2.1-fold when
C. elegans
was cultivated with 2% inoculum as biofilm culture in PMMA-CCF compared to planktonic culture in EF. Biotransformation was enhanced by 7-fold with 10% inoculum. The temporal pattern of biofilm progression based on three-channel fluorescence detection by confocal laser scanning microscopy demonstrated well-developed, stable biofilm with greater colocalization of fluoranthene within extracellular polymeric substances and filaments of the biofilm grown on PMMA in contrast to a glass surface. A bioreactor with discs rotating at 2 revolutions per day affording 6-hourly emersion and immersion mimicked the niche intertidal habitat of
C. elegans
and supported biofilm formation and transformation of fluoranthene. The amount of transformed metabolite was 3.5-fold, biofilm growth was 3-fold, and cytochrome P450 gene expression was 1.9-fold higher in the process mimicking the intertidal conditions than in a submerged process without disc rotation. In the CCF and reactor, where biofilm formation was comparatively greater, higher concentration of exopolysaccharides allowed increased mobilization of fluoranthene within the biofilm with consequential higher gene expression leading to enhanced volumetric productivity.
Acquired Genetic Mechanisms of a Multiresistant Bacterium Isolated from a Treatment Plant Receiving Wastewater from Antibiotic Production
Authors: Johnning Anna , Moore Edward R. B. , Svensson-Stadler Liselott , Shouche Yogesh S. , Larsson D. G. Joakim , Kristiansson Erik
Published: September 2013

The external environment, particularly wastewater treatment plants (WWTPs), where environmental bacteria meet human commensals and pathogens in large numbers, has been highlighted as a potential breeding ground for antibiotic resistance. We have isolated the extensively drug-resistant
Ochrobactrum intermedium
CCUG 57381 from an Indian WWTP receiving industrial wastewater from pharmaceutical production contaminated with high levels of quinolones. Antibiotic susceptibility testing against 47 antibiotics showed that the strain was 4 to >500 times more resistant to sulfonamides, quinolones, tetracyclines, macrolides, and the aminoglycoside streptomycin than the type strain
O. intermedium
LMG 3301
T
. Whole-genome sequencing identified mutations in the Indian strain causing amino acid substitutions in the target enzymes of quinolones. We also characterized three acquired regions containing resistance genes to sulfonamides (
sul1
), tetracyclines [
tet
(
G
) and
tetR
], and chloramphenicol/florfenicol (
floR
). Furthermore, the Indian strain harbored acquired mechanisms for horizontal gene transfer, including a type I mating pair-forming system (MPF
I
), a MOB
P
relaxase, and insertion sequence transposons. Our results highlight that WWTPs serving antibiotic manufacturing may provide nearly ideal conditions for the recruitment of resistance genes into human commensal and pathogenic bacteria.
CelR, an Ortholog of the Diguanylate Cyclase PleD of Caulobacter, Regulates Cellulose Synthesis in Agrobacterium tumefaciens
Authors: Barnhart D. Michael , Su Shengchang , Baccaro Brenna E. , Banta Lois M. , Farrand Stephen K.
Published: September 2013

Cellulose fibrils play a role in attachment of
Agrobacterium tumefaciens
to its plant host. While the genes for cellulose biosynthesis in the bacterium have been identified, little is known concerning the regulation of the process. The signal molecule cyclic di-GMP (c-di-GMP) has been linked to the regulation of exopolysaccharide biosynthesis in many bacterial species, including
A. tumefaciens
. In this study, we identified two putative diguanylate cyclase genes,
celR
(
atu1297
) and
atu1060
, that influence production of cellulose in
A. tumefaciens
. Overexpression of either gene resulted in increased cellulose production, while deletion of
celR
, but not
atu1060
, resulted in decreased cellulose biosynthesis.
celR
overexpression also affected other phenotypes, including biofilm formation, formation of a polar adhesion structure, plant surface attachment, and virulence, suggesting that the gene plays a role in regulating these processes. Analysis of
celR
and Δ
cel
mutants allowed differentiation between phenotypes associated with cellulose production, such as biofilm formation, and phenotypes probably resulting from c-di-GMP signaling, which include polar adhesion, attachment to plant tissue, and virulence. Phylogenetic comparisons suggest that species containing both
celR
and
celA
, which encodes the catalytic subunit of cellulose synthase, adapted the CelR protein to regulate cellulose production while those that lack
celA
use CelR, called PleD, to regulate specific processes associated with polar localization and cell division.
The Sinorhizobium meliloti
ntrX
Gene Is Involved in Succinoglycan Production, Motility, and Symbiotic Nodulation on Alfalfa
Authors: Wang Dong , Xue Haiying , Wang Yiwen , Yin Ruochun , Xie Fang , Luo Li
Published: September 2013

Rhizobia establish a symbiotic relationship with their host legumes to induce the formation of nitrogen-fixing nodules. This process is regulated by many rhizobium regulators, including some two-component regulatory systems (TCSs). NtrY/NtrX, a TCS that was first identified in
Azorhizobium caulinodans
, is required for free-living nitrogen metabolism and symbiotic nodulation on
Sesbania rostrata
. However, its functions in a typical rhizobium such as
Sinorhizobium meliloti
remain unclear. Here we found that the
S. meliloti
response regulator NtrX but not the histidine kinase NtrY is involved in the regulation of exopolysaccharide production, motility, and symbiosis with alfalfa. A plasmid insertion mutant of
ntrX
formed mucous colonies, which overproduced succinoglycan, an exopolysaccharide, by upregulating its biosynthesis genes. This mutant also exhibited motility defects due to reduced flagella and decreased expression of flagellins and regulatory genes. The regulation is independent of the known regulatory systems of ExoR/ExoS/ChvI, EmmABC, and ExpR. Alfalfa plants inoculated with the
ntrX
mutant were small and displayed symptoms of nitrogen starvation. Interestingly, the deletion mutant of
ntrY
showed a phenotype similar to that of the parent strain. These findings demonstrate that the
S. meliloti
NtrX is a new regulator of succinoglycan production and motility that is not genetically coupled with NtrY.
Overexpression of
fetA
(
ybbL
) and
fetB
(
ybbM
), Encoding an Iron Exporter, Enhances Resistance to Oxidative Stress in Escherichia coli
Authors: Nicolaou Sergios A. , Fast Alan G. , Nakamaru-Ogiso Eiko , Papoutsakis Eleftherios T.
Published: September 2013

Reactive oxygen species are generated by redox reactions and the Fenton reaction of H
2
O
2
and iron that generates the hydroxyl radical that causes severe DNA, protein, and lipid damage. We screened
Escherichia coli
genomic libraries to identify a fragment, containing
cueR
,
ybbJ
,
qmcA
,
ybbL
, and
ybbM
, which enhanced resistance to H
2
O
2
stress. We report that the Δ
ybbL
and Δ
ybbM
strains are more susceptible to H
2
O
2
stress than the parent strain and that
ybbL
and
ybbM
overexpression overcomes H
2
O
2
sensitivity. The
ybbL
and
ybbM
genes are predicted to code for an ATP-binding cassette metal transporter, and we demonstrate that YbbM is a membrane protein. We investigated various metals to identify iron as the likely substrate of this transporter. We propose the gene names
fetA
and
fetB
(for Fe transport) and the gene product names FetA and FetB. FetAB allows for increased resistance to oxidative stress in the presence of iron, revealing a role in iron homeostasis. We show that iron overload coupled with H
2
O
2
stress is abrogated by
fetA
and
fetB
overexpression in the parent strain and in the Δ
fur
strain, where iron uptake is deregulated. Furthermore, we utilized whole-cell electron paramagnetic resonance to show that intracellular iron levels in the Δ
fur
strain are decreased by 37% by
fetA
and
fetB
overexpression. Combined, these findings show that
fetA
and
fetB
encode an iron exporter that has a role in enhancing resistance to H
2
O
2
-mediated oxidative stress and can minimize oxidative stress under conditions of iron overload and suggest that FetAB facilitates iron homeostasis to decrease oxidative stress.
Characterization of CpdC, a Large-Ring Lactone-Hydrolyzing Enzyme from Pseudomonas sp. Strain HI-70, and Its Use as a Fusion Tag Facilitating Overproduction of Proteins in Escherichia coli
Authors: Xu Yali , Grosse Stephan , Iwaki Hiroaki , Hasegawa Yoshie , Lau Peter C. K.
Published: September 2013

There are few entries of carbon-carbon bond hydrolases (EC 3.7.1.-) in the ExPASy database. In microbes, these enzymes play an essential role in the metabolism of alicyclic or aromatic compounds as part of the global carbon cycle. CpdC is a ω-pentadecalactone hydrolase derived from the degradation pathway of cyclopentadecanol or cyclopentadecanone by
Pseudomonas
sp. strain HI-70. CpdC was purified to homogeneity and characterized. It is active as a dimer of 56,000 Da with a subunit molecular mass of 33,349. Although CpdC has the highest activity and reaction rate (
k
cat
) toward ω-pentadecalactone, its catalytic efficiency favors lauryl lactone as a substrate. The melting temperature (

T
m

) of CpdC was estimated to be 50.9 ± 0.1°C. The half-life of CpdC at 35°C is several days. By virtue of its high level of expression in
Escherichia coli
, the intact CpdC-encoding gene and progressive 3′-end deletions were employed in the construction of a series of fusion plasmid system. Although we found them in inclusion bodies, proof-of-concept of overproduction of three microbial cutinases of which the genes were otherwise expressed poorly or not at all in
E. coli
was demonstrated. On the other hand, two antigenic proteins, azurin and MPT63, were readily produced in soluble form.