Improvement Strategies in Polyhydroxyalkanoates Production

In a study reported by Doi and co-workers [5], a fed-batch culture technique was applied for copolymer production using Alcaligenes eutrophus in which fructose and ammonium sulfate were fed at a rate of 0.76 and 0.15 g/h respectively. This feeding was then stopped and followed by pentanoic acid feeding at a rate of 0.6 g/h. At the end of the fermentation, 59 mol% of a 3-hydroxyvalerate (3HV) monomer was obtained the cell dry weight (CDW) and PHA content produced was 6.4 g/1 and 65 wt%, respectively. The periodic addition of methanol and n-amyl alcohol under nitrogen limitation to a culture of Paracoccus denitrificans in 3 1 fed-batch cultures resulted in the production of the poly[3-hydroxybutyrate (3HB)-co-3HV] copolymer. About 26% (w/w) containing 60 mol% of the 3HV monomer was obtained after 138 h [6]. 

Koyama and Doi [7] reported the production of copolymer poly(3HB-co-3HV) by Alcaligenes eutrophus from butyric acid and pentanoic acid using fed-batch culture. About 13.5 g of poly(3HB-co-27mol%3HV)/l with 72% of the CDW and high yields were obtained by increasing the carbon-to-nitrogen (C/N) ratio up to 40 mol/mol. A decrease in the C/N ratio resulted in a decrease in polymer synthesis but an increase in 3HV monomer formation. Similar results were obtained using fructose and pentanoic acid whereby a maximum productivity of 0.31 g/l/h of 41 mol% 3HV copolymer (42% of tbe CDW) were obtained [8]. 

Aldrete and co-workers [9] reported the use of a mutant strain of Alcaligenes eutrophus, which has the capability of utilising alcohols, for the production of copolymer poly(3HB-co-3HV) using fed-batch fermentation. The addition of 1-propanol to the medium containing 

A study carried out by Kim and co-workers [10] reported the production of copolymer poly(3HB-co-3HV) by adding propionic acid and glucose to cultures of Ralstonia eutropha during the accumulation phase. During cultivation, the dissolved oxygen concentration was kept at 20% air saturation. An increase in propionic acid to glucose feed ratio from 0.17 to 0.52 mol/mol resulted in an increase in the 3HV monomer composition from 4.3 to 14.3 mol%. However, the author reported a decrease in productivity and yield from 2.55 to 1.64 g/l/h and 0.33 to 0.28 mol/mol, respectively. 

Squio and co-workers [17] reported the production of copolymer poly(3HB-co-3HV) using a phosphate feeding strategy during the production phase in a fed-batch culture phosphate was fed during the production phase in order to maintain a high level of biomass. A production of 63.1 wt% of poly(3HB-co-3HV) with 1.36 g/l/h productivity was obtained compared with 52.2 wt% of poly(3HB-co-3HV) with 1 g/l/h productivity under phosphate depleted conditions. 

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