Engineering Delftia acidovorans DSM39 to produce polyhydroxyalkanoates from slaughterhouse waste.

The inexpensive agricultural fatty by-products could be usefully converted to polyhydroxyalkanoates (PHAs) by properly selected and/or developed microbes. Delftia acidovorans DSM39 is a well-known producer of PHAs with high molar fractions of 4-hydroxybutyrate (4HB), but unable to grow on fatty substrates. The aim of this study was to construct a recombinant strain of D. acidovorans DSM39 using fats-containing waste such as udder, lard and tallow, to produce PHAs. The lipC and lipH genes of Pseudomonas stutzeri BT3, proficient lipolytic isolate, were successfully co-expressed into D. acidovorans DSM39 and the resulting recombinant strain displayed high extracellular enzymatic activity on corn oil. The PHAs production from corn oil achieved high levels (26% of cell dry weight, with about 7% of 4HB). Surprisingly, the recombinant strain produced greater values directly from slaughterhouse residues such as udder and lard (43 and 39%, respectively, with almost 7% of 4HB). Moreover, this work proved the ability of the recombinant D. acidovorans strain to produce PHAs with significant percentage of 4HB, without the supplementation of any precursor in the liquid broth. This research paves the way to the efficient one-step conversion of fatty residues into PHAs having valuable properties exploitable in several medical and industrial applications.

Polyhydroxyalkanoate biosynthesis by Hydrogenophaga pseudoflava DSM1034 from structurally unrelated carbon sources.

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.