Selective Biocatalysis in Bacteria Controlled by Active Membrane Transport

Membrane reactors are attractive when retention of biocatalysts is desirable and when chemical conversion or selectivity can be enhanced by selective permeability of reactants. Unlike polymer or inorganic membranes, biological membranes have transport proteins that use cellular energy to selectively pump components against concentration gradients. This paper analyzes the transport of polynuclear aromatic hydrocarbons (PAHs) across the cell membranes of Pseudomonas fluorescens, an organism that oxidizes aromatic compounds. Experimental data for PAHs were consistent with a model for uptake and energy-dependent transport controlled by the permeability of the outer cell membrane permeability. A model for the enzymatic reaction of mixtures of PAHs showed that energy-dependent transport out of the cell increases the selectivity for the reaction of the less permeable component. Consequently, selective transport may be a useful tool in engineering the metabolism of microorganisms, especially for less hydrophobic compounds with lower permeation rates across biological membranes.