A tunable switch to regulate the synthesis of low and high molecular weight microbial polyesters
✍ Scribed by Richard D. Ashby; Fengying Shi; Richard A. Gross
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 187 KB
- Volume
- 62
- Category
- Article
- ISSN
- 0006-3592
No coin nor oath required. For personal study only.
✦ Synopsis
The addition of poly(ethylene glycol) (M n = 200 g/mol) to the fermentation media of Alcaligenes eutrophus and Alcaligenes latus at various stages of growth resulted in the synthesis of poly(3hydroxybutyrate) (PHB) with bimodal molecular weight distributions. The presence of 2% w/v-PEG-200 did not have deleterious effects on PHB volumetric yields and cell productivity. In general, the M n values of the high (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. latus were varied from 9:91 to 76:24 and from 16:84 to 88:12, respectively. It is believed that the H fractions were formed prior to the addition 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 during 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. latus subsequent to PEG-200 addition consist primarily of chains that have PEG terminal groups. This terminal chain structure was not observed for PHB formed by A. eutrophus.