Autoradiographic determination of mass‐transfer limitations in immobilized cell reactors

Abstract

Pseudomonas putida cells were grown in confined volumes in dual-membrane immobilized cell reactors constructed from microporous polyethylene hollow fibers and silicone rubber tubules as a model system for the study of mass transport in microbial aggregates. Local cell concentrations in the reactors reached 300 g dry mass/L. Pulse-chase radioisotope labeling with (35)SO(4) (2-) was used to estimate the rates of cell mass synthesis and degradation. Sulfur incorporation consistently exceeded sulfur release, implying that the cell mass concentration continually increases. The location and size of the cell growth region was determined using liquid emulsion autoradiography of thin sections prepared from labeled reactors. Cell growth occurs in a region less than 25 mum in depth adjacent to the oxygen supply, and the expansion of the cells caused by cell growth promotes convection of the cell mass into regions of the reactor where starving cells accumulate. The combination of mass-balance and spatial distribution measurements that can be made using radioisotope tracers provides a versatile method for determining metabolic rates and limitations caused by mass transfer in immobilized cell reactors.

Dynamics of artificially immobilizedNitrosomonas europaea: Effect of biomass decay

“…Growth can then be monitored as 32 S activity. Profiles can be observed with a microscope after exposure to an autoradiographic emulsion (Karel and Robertson, 1989). Specific staining of m-RNA has shown to be applicable for monitoring specific degradations in wastewa-ter and soil (Fleming et al, 1993;Jeffrey et al, 1994).…”

Genetic Programming Assisted Stochastic Optimization Strategies for Optimization of Glucose to Gluconic Acid Fermentation

“…Producing gluconic acid by immobilized enzymes is a costly and cumbersome process owing to the difficulties in the immobilization and separation steps; additional difficulties are encountered as a result of denaturization of the enzyme (Rao et al, 1994). In the free-cell fermentation, the mycelia are subjected to various mass and heat-transfer stresses (Karel and Robertson, 1989). Although mechanical agitation helps in alleviating these limitations, it induces a turbulent flow, which may lead to cell disintegration (Wittler et al, 1986), cell breakage or surface erosion (Taguchi et al, 1968), and pellet breakage (Metz and Kossen, 1994).…”

Localization of Lactococcus lactis ssp lactis bv diacetylactis in alginate gel beads affects biomass density and synthesis of several enzymes involved in lactose and citrate metabolism

“…Nevertheless, process development and optimization requires a better understanding of the physiological changes imposed by the microenvironment of cells inside the immobilization matrix. The preferential distribution of included biomass has been previously determined (Karel and Robertson, 1989;Kurosawa et al, 1989;Wijffels and Tramper, 1989), as well as modifications of the composition of immobilized cells in comparison to free cells (Doran and Bailey, 1986). …”