Browsing by Author "Mirpuri, Rajesh G."

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Analysis and characterization of surface oxides on intermetallic alloys of zirconium using auger electron spectroscopy
(Montana State University - Bozeman, College of Engineering, 1991) Mirpuri, Rajesh G.
The effect of bacterial injury on toluene degradation and respiration rates in vapor phase bioreactors
(1997) Jones, Warren L.; Mirpuri, Rajesh G.; Lewandowski, Zbigniew; Cunningham, Alfred B.
The effects of prolonged toluene exposure and degradation on bacterial cultures of Pseudomonas putida 54G were investigated in three reactor systems: a batch suspended culture system, a bench-scale flat plate biofilm reactor, and a bench-scale packed column reactor. Humidified air containing 150 ppmv (toluene limiting) to 750 ppmv (oxygen limiting) toluene vapor was the sole source of carbon and energy supplied to these systems. Results from the suspended batch culture experiments were used to develop rate expressions and kinetic parameters for loss of culturability and of toluene degradative capacity. Experiments in the flat plate reactor were carried out to examine the effects of injury on biofilm structure and function. The packed column studies were performed under conditions relevant to field application, and confirmed results from the other two studies - that decreased culturability on toluene media correlated with decreased specific toluene degradation rate, particularly at higher toluene concentration.
Physiological and chemical gradients in a pseudomonas putida 54g biofilm degrading toluene in a flat plate vapor phase bioreactor
(1997-11) Villaverde, S.; Mirpuri, Rajesh G.; Lewandowski, Zbigniew; Jones, Warren L.
A Pseudomonas putida 54G biofilm was grown on toluene vapor supplied as the sole external carbon and energy source in a flat plate biofilm reactor. Enumerations of cells in the biofilm were made using culture techniques (selective and nonselective for toluene) and microscopic techniques (total and respiring cells), and an analysis of the progression of the state of the culture was made by examination of various fractions of the populations. Long-term exposure to higher levels of toluene produced the following trends: (i) lower fraction of total cells that respired; (ii) lower fraction of culturable cells that also grew on toluene; (iii) higher fraction of respiring cells that could not grow on toluene plates; and (iv) a relatively constant fraction of total cells that could not be cultured on toluene. Respiration rate was determined using oxygen microsensors, and the fraction of the total respiration that was not associated with toluene uptake increased with higher toluene exposure. A combination of cryosectioning and respiration rate data was used to demonstrate that more respiring cells and a higher respiration rate both occurred at the base of the film, suggesting a deterioration in physiological state with continued exposure to toluene. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng56: 361–371, 1997.
Physiological and environmental factors affecting biofilm formation and activity in vapor phase bioreactors
(Montana State University - Bozeman, College of Engineering, 1995) Mirpuri, Rajesh G.
Physiological stress in batch cultures of pseudomonas putida 54g during toluene degradation
(1997-06) Mirpuri, Rajesh G.; Jones, Warren L.; McFeters, Gordon A.; Ridgway, H. F.
Physiological stress associated with toluene exposure in batch cultures of Pseudomonas putida 54G was investigated. P. putida 54G cells were grown using a continuous vapor phase feed stream containing 150 ppmv or 750 ppmv toluene as the sole carbon and energy source. Cells were enumerated on non-selective (R2A agar plates) and a selective minimal medium incubated in the presence of vapor phase toluene (HCMM2). Differential recovery on the two media was used to evaluate bacterial stress, culturability and loss of toluene-degrading capability. A majority of the bacteria were reversibly stressed and could resume active colony formation on selective medium after passage on non-selective medium. A small fraction of the bacterial cells suffered an irreversible loss of toluene degradation capability and were designated as Tol− variants. Numbers of stressed organisms increased with duration of toluene exposure and toluene concentration and coincided with accumulation of metabolic intermediates from incomplete toluene degradation. Respiring cell numbers in the batch cultures decreased as injury increased, indicating a possible relationship between respiring and injured cells. Rate expressions for injury, for formation of Tol− variants and for growth of Tol− variants were determined by calibrating a theoretical model to the results obtained. These rate expressions can be used to calibrate bioreactor models, and provide a basis for better design and control of bioremediation systems.
Predictive model for toluene degradation and microbial phenotypic profiles in flat plate vapor phase bioreactor
(1997-06) Mirpuri, Rajesh G.; Sharp, Robert R.; Lewandowski, Zbigniew; Cunningham, Alfred B.
A predictive model has been developed to describe degradation of toluene in a flat-plate vapor phase bioreactor (VPBR). The VPBR model incorporates kinetic, stoichiometric, injury, and irreversible loss coefficients from suspended culture studies for toluene degradation by P. putida 54G and measured values of Henry's law constant and boundary layer thickness at the gas-liquid and liquid-biofilm interface. The model is used to estimate the performance of the reactor with respect to toluene degradation and to predict profiles of toluene concentration and bacterial physiological state within the biofilm. These results have been compared with experimentally determined values from a flat plate VPBR under electron acceptor and electron donor limiting conditions. The model accurately predicts toluene concentrations in the vapor phase and toluene degradation rate by adjusting only three parameters: biomass density and rates of death and endogenous decay. Qualitatively, the model also predicts gradients in the physiological state cells in the biofilm. This model provides a rational design for predicting an upper limit of toluene degradation capability in a VPBR and is currently being tested to assess applications for predicting performance of bench and pilot-scale column reactors.
Study of toluene degradation kinetics in a flat plate vapor phase bioreactor using oxygen microsensors
(1997) Villaverde, S.; Mirpuri, Rajesh G.; Lewandowski, Zbigniew; Jones, Warren L.
The paper describes the toluene degradation process in a flat plate vapor phase bioreactor (VPBR) by a Pseudomonas putida 54G biofilm. Oxygen microelectrodes were used to measure oxygen concentration profiles through the gas, liquid, and biofilm phases. The linear shape of the dissolved oxygen concentration profile in the outer 87% of the biofilm thickness suggested an absence of reaction in this layer. Oxygen consumption in the remaining basal 13 % (0.3 mm) followed zero order kinetics with a rate constant of 102.2 g m−3 h−1, for toluene gas concentration of 1.5 g m−3. The increase in respiratory activity near the substratum was confirmed by microscopic study of cryogenic biofilm sections, and the lack of activity in the surface film was interpreted as a consequence of injury exerted by the toxic substrate. The accumulation of dead cells on the top of the biofilm contributed a resistance to the transport of substrates to deeper layers of the biofilm suggesting a protective role of the outer layer against the harmful effect of the toxic. These results highlight a new conceptual biofilm model in which both microbial growth and inactivation are controlled by substrate transport, leading to a structure that itself controls substrate availability.
Toluene degradation kinetics for planktonic and biofilm-grown cells of pseudomonas putida 54g
(1997-03) Mirpuri, Rajesh G.; Jones, Warren L.; Bryers, James D.
Toluene degradation kinetics by biofilm and planktonic cells of Pseudomonas putida 54G were compared in this study. Batch degradation of 14C toluene was used to evaluate kinetic parameters for planktonic cells. The kinetic parameters determined for toluene degradation were: specific growth rate, μmax = 10.08 ± 1.2/day; half-saturation constant, KS = 3.98 ± 1.28 mg/L; substrate inhibition constant, KI = 42.78 ± 3.87 mg/L. Biofilm cells, grown on ceramic rings in vapor phase bioreactors, were removed and suspended in batch cultures to calculate 14C toluene degradation rates. Specific activities measured for planktonic and biofilm cells were similar based on toluene degrading cells and total biomass. Long-term toluene exposure reduced specific activities that were based on total biomass for both biofilm and planktonic cells. These results suggest that long-term toluene exposure caused a large portion of the biomass to become inactive, even though the biofilm was not substrate limited. Conversely, specific activities based on numbers of toluene-culturable cells were comparable for both biofilm and planktonically grown cultures. Planktonic cell kinetics are often used in bioreactor models to model substrate degradation and growth of bacteria in biofilms, a procedure we found to be appropriate for this organism. For superior bioreactor design, however, changes in cellular activity that occur during biofilm development should be investigated under conditions relevant to reactor operation before predictive models for bioreactor systems are developed. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng53: 535–546, 1997.