Permeabilization of Escherichia coli cells in the biotransformation of trimethylammonium compounds into l-carnitine

The activity of permeabilized cells of Escherichia coli strains during the biotransformation of trimethylamonium compounds, such as crotonobetaine and d-carnitine, into l-carnitine was determined. Permeabilization of cells did not affect the biotransformation of d-carnitine but improved the yield of l-carnitine obtained when crotonobetaine was used as biotransformation substrate (by nearly two-fold). A higher degree of cell activity with respect to control (45% yield) was observed with organic solvents such as acetone, ethanol, isopropyl alcohol and toluene (65-70% yield), detergents such as Triton X-100 and Tween 20 (70-75% yield) and polyethylenimine (80-89% yield). However, maximum cell activity was attained with 2% of the detergents, Triton X-100 and Tween 20, and 0.1% of polyethylenimine, using a temperature of 37 °C and 10-30 min of treatment time, in which case a yield of 75-89% (100% increase) was obtained with E. coli O44 K74 and 85-94% (80% increase) with E. coli K38 T7-5KE32. Both detergents and polyethylenimine produced alterations in the outer membrane of treated cells since thin-sectioned bacteria were observed by transmision electron microscopy. No l-carnitine dehydratase or carnitine racemase enzyme activity was detected within the extracellular medium when detergents and polyethyleneimine were used. Furthermore, transport studies showed that trimethylammonium compound carriers were not affected by permeabilization, while the rate of l-carnitine transport increased by 20%.