USE OF POLY(ETHYLENE GLYCOL)S TO REGULATE POLY(3-HYDROXYBUTYRATE) MOLECULAR-WEIGHT DURING ALCALIGENES-EUTROPHUS CULTIVATIONS

The ability of poly(ethylene glycol)s, PEGs, to control poly(3-hydroxy butyrate), P3HB, molecular weight in a microbial fermentation polymeri zation process was studied using Alcaligenes eutrophus with fructose a s the sole carbon source. PEGs varying in molecular weight and end gro up functionality were added to the cultivation medium subsequent to ce ll growth, and their effects on polymer formation were evaluated. In g eneral, A. eutrophus showed substantial tolerance for PEGs. This was i llustrated by similar viable cell concentrations for the medium withou t PEG, 10% (w/v) PEG-IO 000 and 2% PEG-800. Furthermore, detrimental e ffects on polymer yields were not observed for concentrations of 5% PE G-106 and 10% PEG-10 000. The greatest reductions in molecular weight were obtained when relatively low molecular weight PEG was added to th e medium. PEG-106 was most effective in that only 0.25% was required t o reduce the number average molecular weight (M(n)) by 74%. The larges t decrease in P3HB M(n) (from 455 000 to 19 400) was observed by addin g 10% PEG-106 to the medium. The largest change in P3HB M(n) per incre mental addition of PEG occurred in the 0-1% PEG concentration range. S upplementing the incubation medium with the monomethoxy ether CH3O-PEG -OH-350 and PEG-300 resulted in almost identical molecular weight redu ctions. However, the dimethoxy ether of tetraethylene glycol was not a n effective agent for molecular weight reduction. Therefore, interacti on between PEG and the PHA production system leading to molecular weig ht reduction was enhanced for lower molecular weight PEGs and required at least one PEG chain end functionality which may be a hydroxyl grou p. It is believed that PEG interacts with the A. eutrophus synthase in such a way to increase the rate of chain termination by water relativ e to chain propagation reactions.