The effect of immobilization on microbial growth and metabolism

Substantial changes in microbial growth and substrate metabolism upon immobilization have been reported for both procaryotic and eucaryotic species of microorganisms. Since a systematic investigation in procaryotes is lacking, and many practical application of microbial growth and metabolism in biochemical engineering involve procaryotic species, the generality and basis of this alteration in microbial activity upon immobilization should be examined.; The objectives of this research were to immobilize environmentally relevant Pseudomonas strains and to test the hypothesis that a shift in cellular properties upon immobilization is the basis of the observed changes in microbial growth and metabolism. An experimental system was developed for evaluation of growth and substrate utilization associated kinetic parameters for suspension cultures and immobilized microorganisms.; Calculations estimating the magnitude of physical phenomenon, such as substrate and oxygen diffusion rates to the cell, and fluid shear effects on the immobilized cell provided the framework for the experimental design. A first order nonlinear rate law was chosen to describe microbial substrate utilization and growth on the substrates 2,4-dichlorophenoxyacetic acid (2,4-D) and toluene. Experimental data followed the kinetics predicted by these rate laws within the substrate range examined. The half saturation constant associated with substrate utilization (K{dollar}sb{lcub}rm d{rcub}{dollar}), the maximum specific substrate utilization rate (k), the organism's maximum specific growth rate ({dollar}musb{lcub}rm max{rcub}{dollar}), and the substrate half saturation constant associated with growth (K{dollar}sb{lcub}rm g{rcub}{dollar}), were determined for each substrate for suspension and immobilized cultures.; Statistical interpretation of cellular reaction rate parameters calculated from the experimental results indicated that only the growth kinetics of the toluene system were significantly altered upon immobilization. The growth associated half saturation constant (K{dollar}sb{lcub}rm g{rcub}{dollar}) for the toluene system increased by thirty fold and the maximum specific growth rate ({dollar}musb{lcub}rm max{rcub}{dollar}) decreased by two fold upon immobilization. Substrate utilization kinetics for both systems were statistically unchanged upon immobilization as were growth associated parameters for the 2,4-D system. These results indicate that a generalized effect of immobilization on microbial growth and metabolism upon attachment does not always occur. Models for substrate utilization and growth kinetics are proposed for the 2,4-D and toluene systems. Implications of these results for environmental applications and bioreactor design are discussed.