SOLUBILIZATION AND GROWTH OF CANDIDA-PSEUDOTROPICALIS IN WATER-IN-OIL MICROEMULSIONS

Some new aspects of microbiology in water-in-oil microemulsions are investigated using Candida pseudotropicalis in a hexadecane solution containing Tween85/Span80 (each 5%, wt:wt) as surfactant, and limited amount of water (up to 3%, vol:vol). Microemulsion solutions containing cells up to 10 mg fresh weight per milliliter can be prepared, which display a greater time stability and a much smaller light scattering than aqueous suspensions having the same cell concentration. This is ascribed to a lower aggregation tendency of the cells in the microemulsion environment. It is also shown that C. pseudotropicalis cells are able to grow (up to a factor of approximately 6-7 within a few days) in the microemulsion system containing nutrient medium in the aqueous microphase; but they are also able to grow at the expense of the hexadecane. This is proved with radioactive-labeled hexadecane by measuring the increase of radioactivity in the cells as well as the emission of (CO2)-C-14. The growth rate of the cells is then compared with the growth rate of cellular proteins during cell reproduction in the microemulsion system. Two regimes are observed: a first one, in which cells growth rate and protein growth rate proceed parallel to each other; and a second one (established after 0.5-1 day) characterized by depletion of proteins in the microemulsion system. The implications of these findings for cell metabolism in microemulsion and for possible biotechnological applications are discussed.