Polyhydroxyalkanoate biosynthesis by Hydrogenophaga pseudoflava DSM1034 from structurally unrelated carbon sources

Abstract

In the present paper we report the exclusive microbial preparation of polyhydroxyalkanoates (PHA) containing 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV) and 4-hydroxybutyrate (4HB) as comonomers through the use of unexpensive carbon sources such as whey from dairy industry. Polymers were produced by growing H. pseudoflava DSM 1034 in minimal medium supplemented with sucrose, lactose or whey without any co-substrate added. The chemical and physical properties of the polymers were fully characterized by GPC, DSC, TGA analyses and the composition by GC and (1)H NMR examinations to especially confirm the content of different monomeric units. The presence of 4HB units into PHA samples is particularly aimed in thermoplastic applications where greater flexibility is required and conventional rigid PHAs tend to fail. Usually the insertion of 4HB into chain backbone consisting of 3-hydroxyalkanoates requires expensive carbon sources mostly of petrochemical origin. According to our study the production of P(3HB-co-3HV-co-4HB) terpolymer can be obtained directly by the use of lactose or waste raw materials such as cheese whey as carbon sources. Although the amount of 4HB in the produced terpolymers was usually low and not exceeding 10% of the total molar composition, a PHA containing 18.4% of 4HB units was produced in 1 step fermentation process from this structurally unrelated carbon sources. The crystallinity of the terpolymer is basically to be markedly affected with respect to that of conventional PHAs, thus obtaining a comparatively less rigid material and easier to be processed.