Biomedical subjects

Bruce E Logan

Publications and source records attributed to Bruce E Logan.

At least 37 records · Page 2Linked to original sources

PubMed2005

Differences between chemisorbed and physisorbed biomolecules on particle deposition to hydrophobic surfaces.

This study examines differences between chemisorbed and physisorbed biomolecules on bacterial adhesion to both hydrophobic and hydrophilic surfaces that are biologically nonspecific. Bacteria-sized latex microspheres were used as a simplified model in order to study these factors that affect microbial adhesion. Two biomolecules (protein A, poly-D-lysine) were covalently bound to microspheres in order to study the effect of proteins on particle filtration rates in columns packed with glass beads. When poly-D-lysine or protein A was covalently bonded to the microspheres, sticking coefficients (a) for the microspheres increased by up to an order of magnitude as compared with uncoated latex microspheres. The glass packing beads were then made hydrophobic by covalently attaching silane groups with different carbon-chain lengths (0.2, 1.2, and 2.8 nm). Sticking coefficients forthe uncoated microspheres on these silanized packing beads (alpha = 0.15 at 1 mM ionic strength; 0.76 at 100 mM) were larger than those on uncoated glass packing beads (0.02 at 1 mM; 0.15 at 100 mM). In addition, adhesion increased with ionic strength on both hydrophobic and hydrophilic surfaces. Physical adsorption gave different results. When either dextran or protein A was physically adsorbed to both the microspheres and the column, no appreciable change in adhesion was observed. Covalently attaching protein A to the microspheres increased their hydrophobicity, but sticking coefficients were large regardless of the substrate hydrophobicity as a result of biomolecule-surface interactions. This study demonstrates that, at high ionic strength, covalently attached hydrophobic species give much higher sticking coefficients for particles than do physically adsorbed species.

Adsorption↗

PubMed2005

Residence time, loading force, pH, and ionic strength affect adhesion forces between colloids and biopolymer-coated surfaces.

Exopolymers are thought to influence bacterial adhesion to surfaces, but the time-dependent nature of molecular-scale interactions of biopolymers with a surface are poorly understood. In this study, the adhesion forces between two proteins and a polysaccharide [Bovine serum albumin (BSA), lysozyme, or dextran] and colloids (uncoated or BSA-coated carboxylated latex microspheres) were analyzed using colloid probe atomic force microscopy (AFM). Increasing the residence time of an uncoated or BSA-coated microsphere on a surface consistently increased the adhesion force measured during retraction of the colloid from the surface, demonstrating the important contribution of polymer rearrangement to increased adhesion force. Increasing the force applied on the colloid (loading force) also increased the adhesion force. For example, at a lower loading force of approximately 0.6 nN there was little adhesion (less than -0.47 nN) measured between a microsphere and the BSA surface for an exposure time up to 10 s. Increasing the loading force to 5.4 nN increased the adhesion force to -4.1 nN for an uncoated microsphere to a BSA surface and to as much as -7.5 nN for a BSA-coated microsphere to a BSA-coated glass surface for a residence time of 10 s. Adhesion forces between colloids and biopolymer surfaces decreased inversely with pH over a pH range of 4.5-10.6, suggesting that hydrogen bonding and a reduction of electrostatic repulsion were dominant mechanisms of adhesion in lower pH solutions. Larger adhesion forces were observed at low (1 mM) versus high ionic strength (100 mM), consistent with previous AFM findings. These results show the importance of polymers for colloid adhesion to surfaces by demonstrating that adhesion forces increase with applied force and detention time, and that changes in the adhesion forces reflect changes in solution chemistry.

Bacterial Adhesion↗

PubMed2005

Power generation in fed-batch microbial fuel cells as a function of ionic strength, temperature, and reactor configuration.

Power density, electrode potential, coulombic efficiency, and energy recovery in single-chamber microbial fuel cells (MFCs) were examined as a function of solution ionic strength, electrode spacing and composition, and temperature. Increasing the solution ionic strength from 100 to 400 mM by adding NaCl increased power output from 720 to 1330 mW/m2. Power generation was also increased from 720 to 1210 mW/m2 by decreasing the distance between the anode and cathode from 4to 2 cm. The power increases due to ionic strength and electrode spacing resulted from a decrease in the internal resistance. Power output was also increased by 68% by replacing the cathode (purchased from a manufacturer) with our own carbon cloth cathode containing the same Pt loading. The performance of conventional anaerobic treatment processes, such as anaerobic digestion, are adversely affected by temperatures below 30 degrees C. However, decreasing the temperature from 32 to 20 degrees C reduced power output by only 9%, primarily as a result of the reduction of the cathode potential. Coulombic efficiencies and overall energy recovery varied as a function of operating conditions, but were a maximum of 61.4 and 15.1% (operating conditions of 32 degrees C, carbon paper cathode, and the solution amended with 300 mM NaCl). These results, which demonstrate that power densities can be increased to over 1 W/m2 by changing the operating conditions or electrode spacing, should lead to further improvements in power generation and energy recovery in single-chamber, air-cathode MFCs.

Bacteria, Anaerobic↗

PubMed2005

Enzymes responsible for chlorate reduction by Pseudomonas sp. are different from those used for perchlorate reduction by Azospira sp.

Pseudomonas sp. PDA is an unusual bacterium due to its ability to respire using chlorate under aerobic conditions. The chlorate reductase produced by PDA was shown to be intrinsically different from the enzyme responsible for chlorate and perchlorate [(per)chlorate] reduction produced by Azospira sp. KJ based on subunit composition and other enzyme properties. The perchlorate reductase from strain KJ appeared to have two subunits (100 and 40 kDa) while the chlorate reductase from PDA had three subunits (60, 48, and 27 kDa). N-terminal amino acid sequencing of the 100 kDa protein from strain KJ showed a 77% similarity with the perchlorate reductase alpha subunit from another perchlorate-respiring bacterium, Dechloromonas agitata, while the N-terminus amino acid sequence of the 60 kDa protein from strain PDA did not show a similarity to previously isolated chlorate or perchlorate reductases.

Amino Acid Sequence↗

PubMed2005

Removal of headspace CO2 increases biological hydrogen production.

For biological hydrogen production by fermentation to be a useful method of hydrogen generation, molar yields of hydrogen must be increased. While heat treatment of a soil inoculum increases hydrogen yields by preventing loss of hydrogen to methanogenesis, hydrogen is still lost to acetic acid generation from hydrogen and CO2. To reduce hydrogen losses via acetogenesis, CO2 concentrations in the headspace were substantially reduced during hydrogen production using a chemical scavenger (KOH). CO2 in the headspace was decreased from 24.5% (control) to a maximum of 5.2% during the highest gas production phase, resulting in a hydrogen partial pressure of 87.4%. This reduction in CO2 increased the hydrogen yield by 43% (from 1.4 to 2.0 mol of H2/mol of glucose). The soluble byproducts in all tests consisted primarily of acetate and ethanol. Higher concentrations of ethanol (10.9 mM) remained in solution from bottles with CO2 removal than in the control (1.2 mM), likely as a result of hydrogen inhibition of biological ethanol conversion to acetic acid. These results show that hydrogen production can be increased by removing CO2 in the reactor vessel, likely as a result of suppression of acetogenesis.

Acetic Acid↗

PubMed2005

Electrochemically assisted microbial production of hydrogen from acetate.

Hydrogen production via bacterial fermentation is currently limited to a maximum of 4 moles of hydrogen per mole of glucose, and under these conditions results in a fermentation end product (acetate; 2 mol/mol glucose) that bacteria are unable to further convert to hydrogen. It is shown here that this biochemical barrier can be circumvented by generating hydrogen gas from acetate using a completely anaerobic microbial fuel cell (MFC). By augmenting the electrochemical potential achieved by bacteria in this MFC with an additional voltage of 250 mV or more, it was possible to produce hydrogen at the cathode directly from the oxidized organic matter. More than 90% of the protons and electrons produced by the bacteria from the oxidation of acetate were recovered as hydrogen gas, with an overall Coulombic efficiency (total recovery of electrons from acetate) of 60-78%. This is equivalent to an overall yield of 2.9 mol H2/mol acetate (assuming 78% Coulombic efficiency and 92% recovery of electrons as hydrogen). This bio-electrochemically assisted microbial system, if combined with hydrogen fermentation that produces 2-3 mol H2/mol glucose, has the potential to produce ca. 8-9 mol H2/mol glucose at an energy cost equivalent to 1.2 mol H2/mol glucose. Production of hydrogen by this anaerobic MFC process is not limited to carbohydrates, as in a fermentation process, as any biodegradable dissolved organic matter can theoretically be used in this process to generate hydrogen from the complete oxidation of organic matter.

Acetates↗

PubMed2005

Interaction forces between colloids and protein-coated surfaces measured using an atomic force microscope.

Bacterial surfaces contain proteins, polysaccharides, and other biopolymers that can affect their adhesion to another surface. To better understand the role of proteins in bacterial adhesion, the interactions between two different model colloids (glass beads and carboxylated latex microspheres) and four proteins covalently bonded to glass surfaces were examined using colloid probes and an atomic force microscope (AFM). Adhesion forces between an uncoated glass colloid probe and protein-coated surfaces, measured in retraction force curves, decreased in the order poly-D-lysine > lysozyme > protein A > BSA. This ordering was consistent with the relative calculated charges of the proteins at neutral pH and the zeta-potentials measured for glass beads and latex microspheres coated with these proteins. When the glass bead was coated with a protein (BSA), overall adhesion forces between the protein-coated colloid and the protein-coated surfaces were reduced, and the adhesion force for each protein decreased in the same order observed in experiments with the uncoated glass bead. When latex colloid probes were coated with BSA, adhesion forces were significantly larger than those measured with BSA-coated glass colloid probes under the same conditions, demonstrating that the nature of the underlying colloid can affect the measured interaction forces. In addition, the adhesion forces measured with the BSA-coated latex colloid increased in a different order (BSA < lysozyme < protein A < poly-D-lysine) than that observed using the BSA-coated glass colloid. It was also found that increasing the solution ionic strength consistently decreased adhesion forces. This result is contrary to the general observation that bacterial adhesion increases with ionic strength. It was speculated that conformational changes of the protein produced this decrease in adhesion with increased ionic strength. These results suggest the need to measure nanoscale adhesion forces in order to understand better molecular scale interactions between colloids and surfaces.

Adsorption↗

PubMed2005

Electricity generation using membrane and salt bridge microbial fuel cells.

Microbial fuel cells (MFCs) can be used to directly generate electricity from the oxidation of dissolved organic matter, but optimization of MFCs will require that we know more about the factors that can increase power output such as the type of proton exchange system which can affect the system internal resistance. Power output in a MFC containing a proton exchange membrane was compared using a pure culture (Geobacter metallireducens) or a mixed culture (wastewater inoculum). Power output with either inoculum was essentially the same, with 40+/-1mW/m2 for G. metallireducens and 38+/-1mW/m2 for the wastewater inoculum. We also examined power output in a MFC with a salt bridge instead of a membrane system. Power output by the salt bridge MFC (inoculated with G. metallireducens) was 2.2mW/m2. The low power output was directly attributed to the higher internal resistance of the salt bridge system (19920+/-50 Ohms) compared to that of the membrane system (1286+/-1Ohms) based on measurements using impedance spectroscopy. In both systems, it was observed that oxygen diffusion from the cathode chamber into the anode chamber was a factor in power generation. Nitrogen gas sparging, L-cysteine (a chemical oxygen scavenger), or suspended cells (biological oxygen scavenger) were used to limit the effects of gas diffusion into the anode chamber. Nitrogen gas sparging, for example, increased overall Coulombic efficiency (47% or 55%) compared to that obtained without gas sparging (19%). These results show that increasing power densities in MFCs will require reducing the internal resistance of the system, and that methods are needed to control the dissolved oxygen flux into the anode chamber in order to increase overall Coulombic efficiency.

Air Pollution↗

PubMed2005

The impact of ultraviolet light on bacterial adhesion to glass and metal oxide-coated surface.

Biofouling of glass and quartz surfaces can be reduced when the surface is coated with photocatalytically active metal oxides, such as TiO2 (anatase form) or SnO2. We measured the attachment of eight strains of bacteria to these two metal oxides (TiO2 and SnO2), and to an uncoated glass (control; designated Si-m) before and after exposure to UV light at wavelengths of 254 nm (UVC) or 340 nm UV (UVA). TiO2-coated surfaces were photocatalytically active at both 254 and 340 nm as evidenced by a decrease in the water contact angle of the surface from 59 degrees +/-2 to <5 degrees. The water contact angle of the SnO2 surface was reduced only at 254 nm, while contact angle of the Si-m glass surface was not altered by light of either wavelength. Bacterial adhesion decreased by 10-50% to photocatalyzed glass surfaces. In all cases, bacteria exposed to the UV light were completely killed due to a combination of exposure to UV light and the photocatalytic activity of the glass surfaces. These results show that UV light irradiation of TiO2-coated surfaces can be an effective method of reducing bacterial adhesion.

Bacillus subtilis↗

PubMed2005

Production of electricity from acetate or butyrate using a single-chamber microbial fuel cell.

Hydrogen can be recovered by fermentation of organic material rich in carbohydrates, but much of the organic matter remains in the form of acetate and butyrate. An alternative to methane production from this organic matter is the direct generation of electricity in a microbial fuel cell (MFC). Electricity generation using a single-chambered MFC was examined using acetate or butyrate. Power generated with acetate (800 mg/L) (506 mW/m2 or 12.7 mW/ L) was up to 66% higher than that fed with butyrate (1000 mg/L) (305 mW/m2 or 7.6 mW/L), demonstrating that acetate is a preferred aqueous substrate for electricity generation in MFCs. Power output as a function of substrate concentration was well described by saturation kinetics, although maximum power densities varied with the circuit load. Maximum power densities and half-saturation constants were Pmax = 661 mW/m2 and Ks = 141 mg/L for acetate (218 ohms) and Pmax = 349 mW/m2 and Ks = 93 mg/L for butyrate (1000 ohms). Similar open circuit potentials were obtained in using acetate (798 mV) or butyrate (795 mV). Current densities measured for stable power outputwere higher for acetate (2.2 A/m2) than those measured in MFCs using butyrate (0.77 A/m2). Cyclic voltammograms suggested that the main mechanism of power production in these batch tests was by direct transfer of electrons to the electrode by bacteria growing on the electrode and not by bacteria-produced mediators. Coulombic efficiencies and overall energy recovery were 10-31 and 3-7% for acetate and 8-15 and 2-5% for butyrate, indicating substantial electron and energy losses to processes other than electricity generation. These results demonstrate that electricity generation is possible from soluble fermentation end products such as acetate and butyrate, but energy recoveries should be increased to improve the overall process performance.

Acetates↗

PubMed2005

Evaluation of procedures to acclimate a microbial fuel cell for electricity production.

A microbial fuel cell (MFC) is a relatively new type of fixed film bioreactor for wastewater treatment, and the most effective methods for inoculation are not well understood. Various techniques to enrich electrochemically active bacteria on an electrode were therefore studied using anaerobic sewage sludge in a two-chambered MFC. With a porous carbon paper anode electrode, 8 mW/m2 of power was generated within 50 h with a Coulombic efficiency (CE) of 40%. When an iron oxide-coated electrode was used, the power and the CE reached 30 mW/m2 and 80%, respectively. A methanogen inhibitor (2-bromoethanesulfonate) increased the CE to 70%. Bacteria in sludge were enriched by serial transfer using a ferric iron medium, but when this enrichment was used in a MFC the power was lower (2 mW/m2) than that obtained with the original inoculum. By applying biofilm scraped from the anode of a working MFC to a new anode electrode, the maximum power was increased to 40 mW/m2. When a second anode was introduced into an operating MFC the acclimation time was not reduced and the total power did not increase. These results suggest that these active inoculating techniques could increase the effectiveness of enrichment, and that start up is most successful when the biofilm is harvested from the anode of an existing MFC and applied to the new anode.

Alkanesulfonic Acids↗

PubMed2005

Electricity generation from cysteine in a microbial fuel cell.

In a microbial fuel cell (MFC), power can be generated from the oxidation of organic matter by bacteria at the anode, with reduction of oxygen at the cathode. Proton exchange membranes used in MFCs are permeable to oxygen, resulting in the diffusion of oxygen into the anode chamber. This could either lower power generation by obligate anaerobes or result in the loss in electron donor from aerobic respiration by facultative or other aerobic bacteria. In order to maintain anaerobic conditions in conventional anaerobic laboratory cultures, chemical oxygen scavengers such as cysteine are commonly used. It is shown here that cysteine can serve as a substrate for electricity generation by bacteria in a MFC. A two-chamber MFC containing a proton exchange membrane was inoculated with an anaerobic marine sediment. Over a period of a few weeks, electricity generation gradually increased to a maximum power density of 19 mW/m(2) (700 or 1000 Omega resistor; 385 mg/L of cysteine). Power output increased to 39 mW/m(2) when cysteine concentrations were increased up to 770 mg/L (493 Omega resistor). The use of a more active cathode with Pt- or Pt-Ru, increased the maximum power from 19 to 33 mW/m(2) demonstrating that cathode efficiency limited power generation. Power was always immediately generated upon addition of fresh medium, but initial power levels consistently increased by ca. 30% during the first 24 h. Electron recovery as electricity was 14% based on complete cysteine oxidation, with an additional 14% (28% total) potentially lost to oxygen diffusion through the proton exchange membrane. 16S rRNA-based analysis of the biofilm on the anode of the MFC indicated that the predominant organisms were Shewanella spp. closely related to Shewanella affinis (37% of 16S rRNA gene sequences recovered in clone libraries).

Bacterial Physiological Phenomena↗

PubMed2005

Hydrogen and electricity production from a food processing wastewater using fermentation and microbial fuel cell technologies.

Hydrogen can be produced from fermentation of sugars in wastewaters, but much of the organic matter remains in solution. We demonstrate here that hydrogen production from a food processing wastewater high in sugar can be linked to electricity generation using a microbial fuel cell (MFC) to achieve more effective wastewater treatment. Grab samples were taken from: plant effluent at two different times during the day (Effluents 1 and 2; 735+/-15 and 3250+/-90 mg-COD/L), an equalization tank (Lagoon; 1670+/-50mg-COD/L), and waste stream containing a high concentration of organic matter (Cereal; 8920+/-150 mg-COD/L). Hydrogen production from the Lagoon and effluent samples was low, with 64+/-16 mL of hydrogen per liter of wastewater (mL/L) for Effluent 1, 21+/-18 mL/L for Effluent 2, and 16+/-2 mL/L for the Lagoon sample. There was substantially greater hydrogen production using the Cereal wastewater (210+/-56 mL/L). Assuming a theoretical maximum yield of 4 mol of hydrogen per mol of glucose, hydrogen yields were 0.61-0.79 mol/mol for the Cereal wastewater, and ranged from 1 to 2.52 mol/mol for the other samples. This suggests a strategy for hydrogen recovery from wastewater based on targeting high-COD and high-sugar wastewaters, recognizing that sugar content alone is an insufficient predictor of hydrogen yields. Preliminary tests with the Cereal wastewater (diluted to 595 mg-COD/L) in a two-chambered MFC demonstrated a maximum of 81+/-7 mW/m(2) (normalized to the anode surface area), or 25+/-2 mA per liter of wastewater, and a final COD of <30 mg/L (95% removal). Using a one-chambered MFC and pre-fermented wastewater, the maximum power density was 371+/-10 mW/m(2) (53.5+/-1.4 mA per liter of wastewater). These results suggest that it is feasible to link biological hydrogen production and electricity producing using MFCs in order to achieve both wastewater treatment and bioenergy production.

Bioelectric Energy Sources↗

PubMed2004

Physical and hydrodynamic properties of flocs produced during biological hydrogen production.

Dense flocs readily form in continuous culture bioreactors used for hydrogen production, but the fractal and hydrodynamic properties of these flocs have not been previously analyzed. We therefore examined the size distribution, fractal dimension, and hydrodynamic properties of flocs formed in a continuous flow, well-mixed reactor treating synthetic wastewater at a fixed condition of a 4.5 h hydraulic detention time (23 degrees C, pH 5.5). The reactor was operated for a total of 3 months at three different organic loading rates (27, 53, and 80 g-COD/L-d) with influent glucose concentrations of 5, 10, and 15 g-COD/L. At all three loading rates the removal of glucose was nearly complete (98.6-99.4%) and biomass was produced in proportion to the organic loading rate (0.86 +/- 0.11, 2.40 +/- 0.26, and 4.59 +/- 1.55 g/L of MLVSS in the reactor). Overall conversion efficiencies of glucose to hydrogen, evaluated on the basis of a maximum of 4 mol-H2/mol-glucose, increased with organic loading rates in the order 17.7%, 23.1%, and 25.6%. The gas contained 56.1 +/- 4.9% hydrogen, with the balance as carbon dioxide. No methane gas was detected. Under these conditions, flocs were produced with mean sizes that increased with organic loading, in the order 0.12 cm (5 g-COD/L), 0.35 cm (10 g-COD/L), and 0.58 cm (15 g-COD/L). As the average floc size increased, the flocs became on average denser and less fractal, with fractal dimensions increasing from 2.11 +/- 0.17 to 2.48 +/- 0.13. Floc porosities ranged from 0.75-0.96, and resulted in aggregate densities that allowed little intra-aggregate flow through the floc. As a result, average settling velocities were not appreciably larger than those predicted by Stokes' law for spherical, impermeable flocs. Our results demonstrate that dense, relatively impermeable flocs are produced in biohydrogen reactors that have settling properties in reasonable agreement with Stokes' law.

Bacteria, Anaerobic↗

PubMed2004

Importance of molecular details in predicting bacterial adhesion to hydrophobic surfaces.

Electrostatic and hydrophobic forces are generally recognized as important in bacterial adhesion. Current continuum models for these forces often wrongly predict measurements of bacterial adhesion forces. The hypothesis tested here is that even qualitative guides to bacterial adhesion often require more than continuum information about hydrophobic forces; they require knowledge about molecular details of the bacteria and substrate surface. In this study, four different strains of bacteria were adsorbed to silica surfaces hydrophobized with alkylsilanes. The thickness of the lipopolysaccharide layers varied on the different bacteria, and the lengths of the alkylsilane molecules were varied from experiment to experiment. Bacterial adhesion was assessed using column experiments and atomic force microscopy (AFM) experiments. Results show that hydrophobized surfaces have higher bacterial sticking coefficients and stronger adhesion forces than bare silica surfaces, as expected. However, adhesion decreased as the solution Debye length became longer than the alkylsilane, perhaps since the silane molecules could not "reach" the bacterial surface. Similarly, those bacteria with a long o-antigen layer had decreased adhesion, perhaps since the silane molecules could not reach surface-bound proteins on the bacteria. This study reveals that macroscopic measurements such as contact angle are not able to fully describe bacterial adhesion; rather, additional details such as the molecular length are required to predict adhesion.

Bacterial Adhesion↗

PubMed2004

Continuous electricity generation from domestic wastewater and organic substrates in a flat plate microbial fuel cell.

A microbial fuel cell (MFC) is a device that converts organic matter to electricity using microorganisms as the biocatalyst. Most MFCs contain two electrodes separated into one or two chambers that are operated as a completely mixed reactor. In this study, a flat plate MFC (FPMFC) was designed to operate as a plug flow reactor (no mixing) using a combined electrode/proton exchange membrane (PEM) system. The reactor consisted of a single channel formed between two nonconductive plates that were separated into two halves by the electrode/PEM assembly. Each electrode was placed on an opposite side of the PEM, with the anode facing the chamber containing the liquid phase and the cathode facing a chamber containing only air. Electricity generation using the FPMFC was examined by continuously feeding a solution containing wastewater, or a specific substrate, into the anode chamber. The system was initially acclimated for 1 month using domestic wastewater orwastewater enriched with a specific substrate such as acetate. Average power density using only domestic wastewater was 72+/-1 mW/m2 at a liquid flow rate of 0.39 mL/min [42% COD (chemical oxygen demand) removal, 1.1 h HRT (hydraulic retention time)]. At a longer HRT = 4.0 h, there was 79% COD removal and an average power density of 43+/-1 mW/m2. Power output was found to be a function of wastewater strength according to a Monod-type relationship, with a half-saturation constant of Ks = 461 or 719 mg COD/L. Power generation was sustained at high rates with several organic substrates (all at approximately 1000 mg COD/L), including glucose (212+/-2 mW/ m2), acetate (286+/-3 mW/m2), butyrate (220+/-1 mW/ m2), dextran (150+/-1 mW/m2), and starch (242+/-3 mW/ m2). These results demonstrate the versatility of power generation in a MFC with a variety of organic substrates and show that power can be generated at a high rate in a continuous flow reactor system.

Bioelectric Energy Sources↗

PubMed2004

Inhibition of aerobic respiration and dissimilatory perchlorate reduction using cyanide.

The effect of low concentrations of cyanide on dissimilatory perchlorate and chlorate reduction and aerobic respiration was examined using pure cultures of Azospira sp. KJ. Cyanide at a concentration of 38 microM inhibited cell growth on perchlorate, chlorate and molecular oxygen, but it did not inhibit the activity of chlorite dismutase. When oxygen accumulation was prevented by adding an oxygen scavenger (Oxyrase or L-cysteine), however, cells completely reduced perchlorate in the presence of cyanide. It was concluded that the inhibition of dissimilative perchlorate reduction by cyanide at this concentration was a consequence of oxygen accumulation, not inhibition of the enzymes used for perchlorate reduction. This finding on the effect of cyanide on respiratory enzymes provides a new method to control and study respiratory enzymes used for perchlorate reduction.

Bacteria, Aerobic↗

PubMed2004

Analysis of bacterial adhesion using a gradient force analysis method and colloid probe atomic force microscopy.

The atomic force microscope (AFM) has been used to examine the stickiness of bacteria on the basis of the analysis of approach and retraction force curves between the AFM tip and the bacterial surface. One difficulty in analyzing approach curve data is that the distance between the AFM tip and the surface of the bacterium is difficult to define. The exact distances are difficult to determine because the surface of the bacterium deforms during force imaging, producing a highly nonlinear region in the approach curve. In this study, AFM approach and retraction curves were obtained using a colloid probe AFM for three strains of Escherichia coli (D21, D21f2, and JM109). These strains differed in their relative adhesion to glass surfaces, on the basis of measurements of sticking coefficients in packed bed flow through column tests. A gradient force curve analysis method was developed to model the interactions between the colloid probe and a surface. Gradient analysis of the approach curve revealed four different regions of colloid-surface interactions during the approach and contact of the probe with the bacterial surface: a noninteraction region, a noncontact phase, a contact phase, and a constant compliance region. The noncontact phase, which ranged from 28 to 59 nm for the three bacterial strains, was hypothesized to arise primarily from steric repulsion of the colloid by extracellular polymers on the bacterial surface. The contact phase, spanning 59-113 nm, was believed to arise from the initial pressure of the colloid on the outer membrane of the cell. The constant compliance region likely reflected the response of the colloid probe to the stiff peptidoglycan layer that confers strength and rigidity to gram negative bacteria. It was shown that the sticking coefficients reported for the three E. coli strains were correlated with the length of the noncontact phase but not the properties of the other phases. Sticking coefficients were also not correlated with any parameters determined from retraction force curves such as pull-off distances or separation energies. These results show that gradient analysis is useful for studying the contribution of the length of the exopolymers on the cell surface to bacterial adhesion to glass surfaces.

Algorithms↗