315회 Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Alc…

315회

연사 : 이 영 하 , 충남대학교 미생물학과

제목:  Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Alcaligenes sp. SH-69 and its mutant

Abstract

It has been of industrial interest to evaluate microbially produced polyhydroxyalkanoates (PHAs) as biodegradable and biocompatible thermoplastics for a wide range of possible applications. Since certain copolymers containing 3-hydroxybutyrate (3HB) and other hydroxy acid monomer units have more useful thermomechanical properties than polyhydroxybutyrate (PHB) homopolymer, interest in the microbial production of copolymers has increased considerably. At present the PHA polyester of great commercial interest is the copolymer of 3HB and 3-hydroxyvalerate [poly(3HB-co-3HV)] which is marketed under the trade name of Biopol.

Ralstonial eutropha (formerly Alcaligenes eutrophus) and many other bacteria have been reported to produce poly(3HB-co-3HV) only when they are grown in media supplemented with such secondary carbon source (cosubstrate) as propionate and valerate, which are incorporated into poly(3HB-co-3HV) via propionyl-CoA and 3-hydroxyvaleryl-CoA, respectively. Increased content of 3HV monomer unit in poly(3HB-co-3HV) with the increasing concentration of cosubstrate has been normally observed. However, the maximum content of 3HV in the copolymer is limited (generally less than 20 mol%) by the toxic effect of cosubstrate at relatively low concentrations. Even though copolymers with high 3HV content are not necessarily more useful than those with low 3HV mol%, alteration of 3HV content in poly(3HB-co-3HV) is desirable from an industrial viewpoint because it may offer the opportunity for the production of different thermoplastics having various degrees of flexibility and toughness.

The distinguishing characteristic of Alcaligenes sp. SH-69, which was isolated from sewage sludge, is that it produces poly(3HB-co-3HV) in culture medium without a cosubstrate. The synthesis of poly(3HB-co-3HV) from a single unrelated substrate is potentially useful since it can address the critical problem of substrate costs as well as allowing easier control of the fermentation process. Alcaligenes sp. SH-69 also produces poly(3HB-co-3HV) with increased 3HV content (11-14 mol%) when 10 mM threonine, isoleucine, or valine are added to the culture medium. In contrast R. eutropha does not utilize these amino acids as a precursor of 3HV. Therefore, it seems likely that Alcaligenes sp. SH-69 has efficient amino acid metabolic pathways in which catabolic metabolites of amino acids converted to the precursors of 3HV.

We are interested in investigating the metabolic pathways leading to poly(3HB-co-3HV) synthesis in Alcaligenes sp. SH-69 so as to develop a new strain which could potentially be useful in the production of poly(3HB-co-3HV) with higher 3HV mol%. In this lecture our recent developments in the production of poly(3HB-co-3HV) copolymers containing 3HV units of more than 50 mol% by a mutant of Alcaligenes sp. SH-69 and the unusual mechanical properties of these copolymers will be presented.