Formation of poly(hydroxybutyrate-co-hydroxyvalerate) by Azotobacter vinelandii UWD

Abstract

Azotobacter vinelandii UWD formed polyhydroxyalkanoate (PHA) copolymers containing 13-hydroxybutyrate and 13-hydroxyvalerate (HV) when grown in a medium containing glucose as the primary C source and valerate (pentanoate) as a precursor. Copolymer was not formed when propionate was added to the glucose medium but was formed when heptanoate, nonanoate, or trans-2-pentenoate was present. Optimal levels of HV were formed when valerate was added at the time of maximum PHA synthesis, although HV incorporation was not dependent on glucose catabolism. IV content in the polymer was increased from 17 to 24 mol% by adding 10 to 40 mM valerate to glucose medium, but HV insertion into the polymer occurred at a fixed rate. Similarly, the addition of valerate to a fed-batch culture of strain UWD in beet molasses in a fermentor produced 19 to 22 g of polymer per liter, containing 8.5 to 23 mol% HV after 38 to 40 h. The synthesis of IV in these cultures also occurred at a fixed rate (2.3 to 2.8 mol% h-'), while the maximum PEIA production rate was 1.1 g liter-' h-1. During synthesis of copolymer in batch or fed-batch culture, the yield from conversion of glucose into PEIA (Yp/s) remained at maximum theoretical efficiency (.0.33 g of PEIA per g of glucose consumed). Up to 45 mol% 1V in the polymer was obtained by growing strain UWD in medium containing c50 mM valerate as the sole C source, but the PHA produced amounted to <1 g/liter. The combination of 30 mM valerate as a sole C source and 0.5 mM 4-pentenoate increased the HV content in the polymer to 52 mol%. The results strongly support a route involving 13-oxidation in the production of 1V in A. vinelandii PEIA. The results show that strain UWD can form PHA copolymers of potential use as bioplastics and that the substrate cost per kilogram of PHA formed in beet molasses medium should be less than half of that per kilogram of PHIA formed in glucose medium.

Production of polyhydroxyalkanoates by Azotobacter vinelandii UWD in beet molasses culture

“…1 g 1-~ hthe rate of HV synthesis was constant (approx. 2.6 mol% h-l), and the YP/s remained at maximum [26]. These results show that a useful range of copolymers can readily be formed by strain UWD growing in BM medium in the fermenter.…”

“…Thus the likely intermediate leading to HV synthesis is the /3-ketoacyl-CoA intermediate prior to thiolysis. This speculation is supported by a detailed study of copolymer synthesis in strain UWD [26], which showed HV synthesis from 2-pentenoate, an intermediate in the/3-oxidation of valerate, and greatly increased HV formation from valerate in the presence of 4-pentenoate, a powerful inhibitor of/3-ketothiolase activity [27].…”

“…Copolymer also has been formed in the fermenter, by the feeding of valerate to strain UWD during polymer synthesis in BM medium [26]. The addition at 24 h of sufficient valerate to give a 10 mM final concentration in the fermenter resulted in the synthesis of 8.5 mol% HV in the polymer, but this decreased with time as HV synthesis was overcome by continued HB synthesis.…”

Sequential Feeding of Glucose and Valerate in a Fed-Batch Culture of Ralstonia eutropha for Production of Poly(hydroxybutyrate-co-hydroxyvalerate) with High 3-Hydroxyvalerate Fraction

“…P(3HB-co-3HV) has been produced in the cultivations of Ralstonia eutropha (R. eutropha) (5,(9)(10)(11), recombinant Escherichia coli (E. coli) (12,13), Paracoccus denitrificans and Methylobacterium extorquens (14), Azotobater vinelandii (A. vinelandii) UWD (15), A. latus (16), and Alcaligenes Sp. SH-69 (17) with several different carbon sources such as glucose and propionate, glucose and valerate, methanol and n-amyl alcohol, sucrose and valerate, butyrate and valerate, or only glucose, propanol, and valerate, etc.…”

Production of poly‐3‐hydroxybutyrate from lactose and whey by Methylobacterium sp. ZP24

“…In PHA production by fermentation, the substrate and recovery costs are high, making their use unattractive. Page and his coworkers, using Azotobacter vinelandii UWD, have shown a substantial reduction in raw material cost using beet molasses (Page 1992 ;Page et al 1992).…”