Browsing by Author "Mueller, Robert Franz"

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Bacterial transport and colonization in low nutrient environments
(1996-11) Mueller, Robert Franz
Crucial and potentially rate limiting events in biofilm formation are the transport of microorganisms to the solid-water interface and the subsequent attachment onto a substratum. If these attached cells find suitable environmental conditions they will replicate, grow and form a biofilm. Experiments with different surfaces—stainless steel, glass, and polycarbonate—and two Pseudomonas species were conducted and parameters describing attachment, growth, and transport were measured in situ and in real time using image analysis techniques. The phenomenon of cellular starvation was investigated with special attention to the effect on the attachment characteristics of the two tested Pseudomonas species. Experiments were conducted with Pseudomonas aeruginosa and Pseudomonas fluorescens as a Mot+ and a Mot− strain. As a result of superior transport properties, flagellated cells of Pseudomonas fluorescens colonized a substratum at a higher rate than unflagellated cells. Nutrient conditions in the bulk water influenced the growth of suspended and attached organisms, as well as the cellular transport to the solid-water interface and the rate of attachment onto the substratum. Starved cells of P. aeruginosa and P. fluorescens exhibited increased cell motility by size reduction. Cellular transport was demonstrated to be a crucial process in microbial colonization, and may be limiting the overall rate of surface colonization. The phenomenon was demonstrated for a motile and nonmotile mutant of the same strain. Hence, diffusive, advective, and hydrodynamic properties of a specific system cannot be neglected if we try to understand and simulate microbial colonization. Keywords
Characterization of initial events in bacterial surface colonization by two pseudomonas species using image analysis
(1992-05) Mueller, Robert Franz; Characklis, William G.; Jones, Warren L.; Spears, J.
The processes leading to bacterial colonization on solidwater interfaces are adsorption, desorption, growth, and erosion. These processes have been measured individually in situ in a flowing system in real time using image analysis. Four different substrata (copper, silicon, 316 stainless-steel and glass) and 2 different bacterial species (Pseudomonas aeruginosa and Pseudomonas fluorescens) were used in the experiments. The flow was laminar (Re = 1.4) and the shear stress was kept constant during all experiments at 0.75 N m−2. The surface roughness varied among the substrata from 0.002 μm (for silicon) to 0.015 μm (for copper). Surface free energies varied from 25.1 dynes cm−1 for silicon to 31.2 dynes cm−1 for copper. Cell curface hydrophobicity, reported as hydrocarbon partitioning values, ranged from 0.67 for Ps. fluorescensto 0.97 for Ps. aeruginosa. The adsorption rate coefficient varried by as much as a factor of 10 among the combinations of bacterial strain and substratum material, and was positively correlated with surface free energy, the surface roughness of the substratum, and the hydrophobicity of the cells. The probability of desorption decreased with increasing surface free energy and surface roughness of the substratum. Cell growth was inhibited on copper, but replication of cells overlying an initial cell layer was observed with increased exposure time to the cell-containing bulk water. A mathematical model describing cell accumulation on a substratum is presented.
Characterization of initial events of bacterial colonization at solid-water interfaces using image analysis
(Montana State University - Bozeman, College of Engineering, 1990) Mueller, Robert Franz
Characterization of thermophilic consortia from two souring oil reservoirs
(1996-09) Mueller, Robert Franz; Nielsen, P. H.
Inhibition of anaerobic digestion caused by heavy metals
(1992) Mueller, Robert Franz; Steiner, A.
The severity of heavy metal inhibition on anaerobic digestion is dependent on the metal species and their dissolved concentration in the digester. The general sequence of inhibition on anaerobic digestion of municipal sewage sludge was found with Ni > Cu > Cd > Cr > Pb. Metal immobilization affinity in the sludge followed the reverse sequence. Due to sulfide production during digestion high quantities of heavy metals are precipitating as highly insoluble sulfide salts. Nickel was immobilized to 94 % in the digester and indicated the most dramatic effect on anaerobic digestion. At a concentration of 250 to 300 g Ni m-3 toxicity occurred. Lower nickel concentrations resulted in reversible process inhibition. Copper up to 1000 g Cu m-3 caused reversible inhibition of acid producing, fermentative, and methanogenic bacteria. The time necessary for recovery of the process was dependent on the initial copper concentration in the digester. The organisms indicated capability of adaptation to copper. The copper uptake in the digester was 97 %. Cadmium inhibited digestion of sewage sludge up to approximately 50 % at 650 g Cd m-3. For long durations of acclimation a tendency toward recovery was observed. The cadmium uptake in the digested sludge was 99 %. Chromium and lead were uptaken at 99.9 % during digestion. Hence, the addition of these metals up to 1000 mg Cr/l and 600 mg Pb/l showed only little effect on anaerobic digestion.
Kinetic analysis of microbial sulfate reduction by desulfovibrio desulfuricans in an anaerobic upflow porous media biofilm reactor
(1994-02) Chen, Ching-I; Mueller, Robert Franz; Griebe, Thomas
An anaerobic upflow porous media biofilm reactor was designed to study the kinetics and stoichiometry of hydrogen sulfide production by the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans (ATCC 5575) as the first step for the modeling and control of formation souring (H2S) in oil field porous media. The reactor was a packed bed (50 × 5.5 cm) tubular reactor. Sea sand (140 to 375 μm) was used as the porous media. The initial indication of souring was the appearance of well-separated black spots (precipitates of iron sulfide) in the sand bed. The blackened zones expanded radially and upward through the column. New spots also appeared and expanded into the cone shapes. Lactate (substrate) was depleted and hydrogen sulfide appeared in the effluent. Analysis of the pseudo–steady state column shows that there were concentration gradients for lactate and hydrogen sulfide along the column. The results indicate that most of the lactate was consumed at the front part of the column. Measurements of SRB biomass on the solid phase (sand) and in the liquid phase indicate that the maximum concentration of SRB biomass resided at the front part of the column while the maximum in the liquid phase occurred further downstream. The stoichiometry regarding lactate consumption and hydrogen sulfide production observed in the porous media reactor was different from that in a chemostat. After analyzing the radial dispersion coefficient for the SRB in porous media and kinetics of microbial growth, it was deduced that transport phenomena dominate the souring process in our porous media reactor system.
Kinetic investigation of microbial souring in porous media using microbial consortia from oil reservoirs
(1994-07) Chen, Ching-I; Reinsel, Mark A.; Mueller, Robert Franz
Microbial souring (H2S production) in porous media was investigated in an anaerobic upflow porous media reactor at 60°C using microbial consortia obtained from oil reservoirs. Multiple carbon sources (formate, acetate, propionate, iso- and n-butyrates) found in reservoir waters as well as sulfate as the electron acceptor was used. Kinetics and rates of souring in the reactor system were analyzed. Higher volumetric substrate consumption rates (organic acids and sulfate) and a higher volumetric H2S production rate were found at the from part of the reactor column after H2S production had stabilized. Concentration gradients for the substrates (organic acids and sulfate) and H2S were generated along the column. Biomass accumulation throughout the entire column was observed. The average specific sulfate reduction rate (H2S production rate) in the present reactor after H2S production had stabilized was calculated to be 11062 ±2.22 mg sulfate-S/day g biomass. © 1994 John Wiley & Sons, Inc.
Microbial dynamics in souring oil reservoirs
(Montana State University - Bozeman, College of Engineering, 1994) Mueller, Robert Franz