Toxicity effects of compressed and supercritical solvents on thermophilic microbial metabolism

Selection of biocompatible solvents is critical when designing bioprocessin g applications for the in situ biphasic extraction of metabolic end-product s. The prediction of the biocompatibility of supercritical and compressed s olvents is more complicated than for liquid solvents, because their propert ies can change significantly with pressure and temperature. The activity of the anaerobic thermophilic bacterium, Clostridium thermocellum, was studie d when the organism was incubated in the presence of compressed nitrogen, e thane, and propane at 333 K and multiple pressures. The metabolic activity of the organisms in contact with compressed solvents was analyzed using tra ditional indicators of solvent biocompatibility, such as log P, interfacial tension, and solvent density. The toxicity of the compressed solvents was compared with the phase and molecular toxicity effects measured in liquid a lkanes at atmospheric pressure. Inactivation increased with time in the pre sence of the compressed solvents, but was constant in the presence of atmos pheric liquid solvents. Knowledge of molecular and phase toxicity provides a framework for the interpretation of C. thermocellum metabolism in contact With atmospheric and compressed solvents. (C) 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 70: 491-497, 2000.