Campbell W. Robinson

Review: Optimizing inducer and culture conditions for expression of foreign proteins under the control of thelac promoter

This review examines factors which influence the expression of foreign proteins inEscherichia coli under the transcriptional control of thelac andtac promoters, and discusses conditions for maximizing the production of a foreign protein using this system. Specifically, the influence of IPTG (isopropyl-β-d-thiogalactoside) concentration, temperature, composition of the growth medium, the point in the growth curve at which cells are induced with either IPTG or lactose, and the duration of the induction phase are discussed.

Measurement of rheological properties of filamentous fermentation broths

It is well established that fermentation broths of filamentous microorganisms possess viscous non-Newtonian rheological properties. Despite the industrial significance of these broths and their fermentation products, the correct application of rheological measurement methodologies to filamentous broths and the influence of broth rheology on transport phenomena in bioreactors is poorly understood. In this work, the rheological properties of broths of the filamentous microorganisms Aspergillus niger, Penicillium chrysogenum and Streptomyces levoris grown on soluble substrates were studied. Three different types of viscometers were used: (1) three on-line pipeline viscometers (5.8, 11.6 and 15.4 mm i.d.); (2) two rotating cylinder viscometers (Haake model RV12, MV2 and MV3 sensors), and (3) helical ribbon and turbine impeller viscometers. Results obtained with all three viscometer types showed increasing pseudoplastic behaviour (power law parameters from MV2 viscometer data: 0.3 ⩽n⩽1; 0.001 ⩽K ⩽5 Pa.sn) and yield stress (0⩽ty⩽16 Pa) with increasing biomass concentration(up to 20 g dw/1). Comparison of measurements at equivalent shear rates revealed lower measured apparent viscosities for the smallest pipeline viscometer, thus indicating the presence of wall “slip”. In contrast, higher apparent viscosities were observed with the turbine impeller, leading to the conclusion that the commonly made assumption that the average shear rate in this type of viscometer is independent of fluid rheology is not valid. Reasonable agreement was obtained among rheological measurements made on the large (≳ 11.6 mm i.d..) pipelines, the helical ribbon impeller and two different diameter rotating cylinder viscometers (provided the yield stress was exceeded inside the cup/bob gap); this suggests that “slip” effects were not significant in these viscometers. Based on these results,recommendations are provided to assist in the selection of appropriate viscometers for application to heterogeneous, non-Newtonian fermentation broths.

Pentachlorophenol adsorption and desorption characteristics of granular activated carbon—I. Isotherms

The kinetics of pentachlorophenol (PCP) adsorption/desorption with Calgon F300 granular activated carbon (GAC) was studied. A previously-developed model of GAC adsorption/desorption kinetics was applied to the case of PCP for both batch and continuous plug-flow liquid conditions. The model predictions were found to be in good agreement with the experimental observations.

PHENOL DEGRADATION BY A PSYCHROTROPHIC STRAIN OF PSEUDOMONAS PUTIDA

SummaryCell growth and phenol degradation kinetics were studied at 10°C for a psychrotrophic bacterium, Pseudomonas putida Q5. The batch studies were conducted for initial phenol concentrations, So, ranging from 14 to 1000 mg/1. The experimental data for 14<=So<=200 mg/1 were fitted by non-linear regression to the integrated Haldane substrate inhibition growth rate model. The values of the kinetic parameters were found to be: μm=0.119 h−1, KS=5.27 mg/1 and KI=377 mg/1. The yield factor of dry biomass from substrate consumed was Y=0.55. Compared to mesophilic pseudomonads previously studied, the psychrotrophic strain grows on and degrades phenol at rates that are ca. 65–80% lower. However, use of the psychrotrophic microorganism may still be economically advantageous for waste-water treatment processes installed in cold climatic regions, and in cases where influent waste-water temperatures exhibit seasonal variation in the range 10–30°C.

Application of airlift gas-liquid-solid reactors in biotechnology

Abstract Airlift reactors are pneumatically agitated reactors with circulation in a defined cyclic pattern through a loop of conduits. The possibility of providing the required aeration and agitation during fermentation processes, with low energy input, has brought a flourishing of industrial interest in airlift reactors. Due to the mildness and uniformity of turbulence in airlift reactors compared to conventional reactors, such as stirred tank reactors and bubble columns, particular interest is being focused on airlift reactors for use with various cell cultures. This paper presents an overview of the current state of knowledge in airlift reactor design and operation with a focus on external-loop airlift reactors. Emphasis is placed on a discussion of macroscale liquid circulation velocity because it is this parameter which distinguishes airlift reactors from other pneumatically agitated reactors, such as bubble columns. In addition, specific areas where gaps presently exist in the knowledge of airlift reactor design, operation, and scale-up are identified and recommendations are made for future research.

Prediction of the volumetric mass transfer coefficient in pneumatic contactors

Semi-theoretical expressions are developed for the prediction of the volumetric mass transfer coefficient, (KLaD)T, in pneumatic contactors, using the correlation of Calderbank and Moo-Young Chem. Engng Sci.16, 39 (1961) for the mass transfer coefficient and the local isotropic turbulence theory for predicting bubble diameter. A direct proportionality of (KLaD)T to the gas hold-up is predicted, with an exponent of 1.2 on eG, while, in terms of physical parameters, (KLaD)T is predicted to be proportional to the 0.8 power of the superficial gas velocity for both bubble column and airlift contactors, and proportional to (1 + Ad/Ar)−2 for airlift contactors, where Ad/Ar is the downcomer-to-riser cross-sectional area ratio. Experimental results obtained in bubble column and airlift contactors (external-loop and concentric-tube) of pilot-plant scale (ca. 50L liquid capacity), with water and 0.15 kmol m−3 NaCl solution as liquid media, were used to test the proposed expressions.

Effect of temperature on the inhibition kinetics of phenol biodegradation by Pseudomonas putida Q5

The temperature-dependent performance of mixed-culture wastewater treatment processes may be strongly influenced by their content of psychrotrophic bacteria. In this work, the effect of temperature on cell growth and phenol biodegradation kinetics of the psychrotrophic bacterium Pseudomonas putida Q5 were determined using both batch and continuous cultures in the range of 10-25 degrees C. The Haldane equation was found to be the most suitable substrate-inhibition model for the specific growth rate. The Haldane parameters mu(max) and K(I) were best modeled by a square-root dependency on temperature. However, the Arrhenius model provided a better prediction of the temperature dependence of K(S). The variation of the yield constant with temperature also was studied experimentally. Comparisons with results of previous workers are presented.

Kinetics of the simultaneous batch degradation of p-cresol and phenol by Pseudomonas putida

SummaryThe kinetics of the batch degradation of phenol and p-cresol in a dual-substrate system by Pseudomonas putida was investigated. A model was developed which was able to successfully predict phenol and p-cresol levels during batch growth. A constant specific growth rate (μ) was assumed together with the assumption that the biomass yield factors (Y) for growth on phenol and p-cresol were identical. These simplifying assumptions allowed an analytical solution to the model equations to be easily obtained, as well as reducing the number of unknown parameters that required estimation. Phenol and p-cresol were metabolized simultaneously by P. putida. P. putida did not appear to metabolize either of the two substrates preferentially. The rate of utilization of aparticular organic substrate was related to its fraction of the total organic substrate present, i.e., for substrate 1 the assimilation rate depended on S1/(S1+S2), where Siis the concentration of the ith substrate.

A microbial regeneration process for granular activated carbon—II. regeneration studies

Abstract The in situ biological regeneration of an activated carbon adsorber was investigated. Experimental results are given for a single-solute system containing phenol and a bisolute system containing phenol and p-cresol, both of which were regenerated using a mono-culture of Pseudomonas putida. The performance of an activated carbon adsorber that was bioregenerated up to six times was evaluated on the basis of the breakthough of phenolics during each intervening continuous-flow adsorption period. For both the regeneration and the loading cycles, predictions of system behaviour based on the bioregeneration model of Hutchinson and Robinson (1990) agreed well with experimental observations. Carbon particle internal diffusional resistances were found to be rate limiting during most of the regeneration cycle. The breakthough performance of the bioregenerated carbon was found to deteriorate with each successive regeneration. Microbial fouling of the column during bioregeneration was found to produce a marked deterioration in the subsequent breakthrough performance of the bioregenerated activated carbon.

Immobilization of yeast cells on various supports for ethanol production

An immobilization technique has been developed for a packed bed fermenter which is being considered as one stage of a process for the production of fuel-grade ethanol from sugar solutions. Relatively inexpensive beech wood chips have been successfully used as the support material and relatively high cell loadings of 188 mg DW cells/g DW support have been achieved for a test system of Saccharomyces cerevisiae cultures.No washout of adsorbed cells occurs below a superficial liquid velocity of 8.9 × 10-2 cm/s which can be increased to 9.7 × 10-2 cm/s by including up to 1% Hercofloc solution in the reactor medium during the immobilization procedure. The immobilization procedure is practically unaffected by pH and temperature in the range 3.5 to 5.0 and 22 °C to 37 °C respectively.Typical ethanol productivity of 21.8g/l·hr has been obtained with wood-chip-adsorbed cells, which compares well with optimal values of 18 to 32g/l·hr obtained using free-suspension cultures in stirred-tank fermenters with cell recycle.