A TUNABLE SWITCH TO REGULATE THE SYNTHESIS OF LOW AND HIGH-MOLECULAR-WEIGHT MICROBIAL POLYESTERS

The addition of poly(ethylene glycol) (M-n = 200 g/mol) (PEG-200) to t he fermentation media of Alcaligenes eutrophus and Alcaligenes latus a t various stages of growth resulted in the synthesis of poly(3-hydroxy butyrate) (PHB) with bimodal molecular weight distributions. The prese nce of 2% w/v-PEG-200 did not have deleterious effects on PHB volumetr ic yields and cell productivity. In general, the M-n values of the hig h (H) and low (L) fractions showed little variability as a function of the time at which PEG-200 was added to the cultures. By this approach , the H:L ratios (w/w) of the PHB synthesized by A. eutrophus and A. l atus were varied from 9:91 to 76:24 and from 16:84 to 88:12, respectiv ely. It is believed that the H fractions were formed prior to the addi tion of PEG-200 to the cultures. Also, once PEG-200 was made available to the cells, PEG-200 acted as a switch so that the reduced molecular weight fraction was formed. In addition, a necessary requirement for the above is that the frequency of transesterification reactions durin g polymer synthesis was small. The efficiency that PEG-200 reduced the molecular weight of the PHBs formed by both bacteria appears similar. Indirect evidence suggests that the PHB L fractions formed by A. latu s subsequent to PEG-200 addition consist primarily of chains that have PEG terminal groups. This terminal chain structure was not observed f or PHB formed by A. eutrophus. (C) 1999 John Wiley & Sons, Inc. Biotec hnol Bioeng 62:106-113,1999.