P45: Production of Polyhydroxyalkanoates by Ralstonia eutropha from Inexpensive Substrates

Polyhydroxyalkanoates (PHAs) have been drawing much attention because of their potential use as biodegradable thermoplastics. The use of PHAs as substitutes for conventional non-degradable plastics in a wide range of applications has been hampered by the high production cost of PHAs compared with those of petrochemical-based polymers. Vegetable oils are desirable feedstocks for PHA production because they are inexpensive and the theoretical yield coefficients are as high as over 1.0 g-PHA per g- vegetable oils used. Volatile fatty acids (VFAs) are produced by anaerobic treatment of food wastes and can also be utilized as inexpensive substrates for PHA synthesis. In this study, several Ralstonia eutropha strains were grown on the mixture of VFAs (acetic, propionic, and butyric acid) as carbon and energy source for growth and PHA synthesis. R. eutropha KCTC 2658 accumulated the highest amounts of PHAs up to 50% of dry cell weight from total 5 g/L of VFAs (acetic acid : propionic acid : butyric acid = 1:2:2) as carbon source. Copolymers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) up to 35 mol% 3HV were produced by feeding mixed VFAs. Batch culture kinetics showed that butyric acid was consumed first with cell growth and then propionic acid was consumed resulting in an increase in 3HV fraction. A homopolymer of P(3HB) was produced from soybean oil as a sole carbon source by batch and fed-batch culture of R. eutropha KCTC 2662 with dry cell weight of 17~37 g/L, PHA content of 80~83 wt%, and a high yield of 0.75~0.84 g-PHA/g-oil.