HIGH CELL-DENSITY FERMENTATIONS OF PSEUDOMONAS-OLEOVORANS FOR THE PRODUCTION OF MCL-PHAS IN 2-LIQUID PHASE MEDIA

Pseudomonas oleovorans is able to produce medium-chain length poly(3-h ydroxyalkanoates) (mcl-PHA) in continuous and fed-batch two-liquid pha se fermentations using n-octane as a sole carbon and energy source. We have previously shown that it is possible to increase the volumetric productivity of such a system by increasing the concentration of cells and PHA in the fermentor with maximal production limited by the oxyge n transfer rate to the cultures in our bioreactor systems and by compl ex effects of metal ions on biomass yields, leading to a maximal bioma ss concentration of 37 g l(-1). This paper describes further improveme nts in the cultivation process of P. oleovorans for the production of mcl-PHA in two-liquid phase fermentations that have led to a threefold higher final cell density. In order to further increase cell densitie s, we determined the growth yields for each of the metal ions and deve loped an optimized feed of metals. Using a bioreactor with better oxyg en transfer capabilities, we were able to increase the final cell dens ity in fed-batch cultivations rep to 90 g biomass l(-1). By applying a computer-controlled exponential nitrogen feed in combination with the feeding of various metal ions, a cell density of 112 g l(-1) was obta ined. The PHA content of these cells decreased as the cell density inc reased above 40-50 g l(-1), thus negatively affecting overall PHA yiel ds and productivities. Possible approaches to reducing these PHA losse s are discussed. (C) 1998 Elsevier Science Inc.