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 (14)CO(2). 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.

Photosynthetic activity of cyanobacteria in water-in-oil microemulsions.

The solubilization and the photosynthetic activity of cyanobacteria (Anabaena variabilis) in water-in-oil microemulsions consisting of (Tween85/Span80)/hexadecane/water is investigated. Transparent and stable solutions containing up to 10(8) cells/mL could be obtained. The physical state and stability of the cells in the microemulsion, as evidenced from optical and electron microscopy, is dependent upon the physical parameters of the system, and in particular on the hydrophilic-lypophilic balance (HLB) of the surfactant system. Conditions could be found, under which the cells in the microemulsion system display photosynthetic activity This was judged by measuring polarographically the oxygen evolution and by studying the photosynthetic activity in the presence of specific inhibitors.