Use of poly(ethylene glycol) to control the end group structure and molecular weight of poly(3-hydroxybutyrate) formed by Alcaligenes latus DSM 1122

Poly(ethylene glycol), PEG, which is known to associate with lipid membranes and proteins, was used to control the molecular weight and end-group structure of poly(3-hydroxybutyrate), P3HB, produced by Alcaligenes latus DSM 1122. A series of PEGs with varying molecular weights (PEG-106 to PEG-10,000) was added to the A. latus incubation medium. In general, PEGs of relatively lower molecular weight and high concentrations of PEG in the medium had deleterious effects on cell growth, polymer yield and P3HB productivity. PEGs with molecular weights at or below 1000 g/mol resulted in the formation of P3HB with reduced molecular weights. The extent of molecular weight reduction was dependent on the concentration and molecular weight of the PEG added to the incubation medium. Larger molecular weight reductions at identical medium concentrations were achieved by using PEG of relatively fewer molecular weight. PEG-106 was most effective in regulating P3HB molecular weight in that only a 1% (w/v) medium concentration was required to reduce the number average molecular weight (M-n) by 89% (from 267,000 to -30,000 g/mol). Study of the purified polymers showed that for PEG molecular weights up to 1,000 g/mol, P3HB chains were esterified at their carboxyl terminus with PEG chain segments. Thus, products having ''tailored'' molecular weights and end-group structure were formed. This was explained by that for P3HB formation by A. latus, PEG of sufficiently low molecular weight served as a chain terminating agent. In other words, the in-vivo esterification of P3HB chain ends with PEG increases the rate of chain termination relative to propagation and, thereby, results in reduced P3HB molecular weight. (C) 1997 Elsevier Science Ltd.