MEDIUM-CHAIN LENGTH ALKANE SOLVENT-CELL TRANSFER RATES IN 2-LIQUID PHASE, PSEUDOMONAS-OLEOVORANS CULTURES

The oxidation of medium chain length alkanes and alkenes (C6 to C12) b y Pseudomonas oleovorans and related, biocatalytically active recombin ant organisms, in two-liquid phase cultures can be used for the bioche mical production of several interesting fine chemicals. The volumetric productivities that can be attained in two-liquid phase systems can b e, in contrast to aqueous fermentations, limited by the transport of s ubstrates from an apolar phase to the cells residing in the aqueous ph ase and by toxic effects of apolar solvents on microbial cells. We hav e assessed the impact of these possible limitations on attainable prod uctivities in two-liquid phase fermentations operated with mcl-alkanes . Pseudomonas oleovorans grows well in two-liquid phase media containi ng a bulk n-octane phase as the sole carbon source. However, cells are also damaged, typically resulting in a cell lysis rate of about 0.08 to 0.10 h(-1). These rates could be lowered by 50 to 70% to 0.03 h(-1) and substrate yields increased from 0.55 to 0.85 g g(-1) by diluting octane in non-metabolizable long-chain hydrocarbon solvents. Transfer rates of medium chain length (mcl) alkanes from the apolar phase to th e cells were determined by following growth and the rate at which carb on-containing metabolites accumulated in the different phases of the c ultures. mcl-Alkane solvent-cell transfer rates of at least 79, 64, an d 18 mmol per liter of aqueous medium per hour were determined for n-h eptane, n-octane, and n-decane, respectively. Rates of up to 30 mmol L -l h-l were observed under octane-limiting conditions in systems where the apolar substrate was dissolved to concentrations below 3% (v/v) i n hexadecene. Based on low power input experiments, we estimated the m aximum obtainable mass transfer rates in large scale processes to be i n the range of 13 mmol L-1 h(-1) for decane and higher than 45 mmol L- 1 h(-1) for octane and heptane. The results indicate that high solvent to cell mass transfer rates and minimized cell damage will enable hig h production rates in two-liquid phase bioprocesses, justifying ongoin g efforts to attain high densities of catalytically, highly active cel ls in such systems. (C) 1998 John Wiley & Sons, Inc.