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T. Lütke-Eversloh1,2, and A. Steinbüchel1
1 Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität Münster, Corrensstraße 3, 48149 Münster, Germany
2 Present address: Massachusetts Institute of Technology, Department of Chemical Engineering, 77 Massachusetts Avenue, Room 56422, Cambridge MA 021394307, USA
Polythioesters (PTEs) were discovered recently as a novel class of biopolymers, which are exclusively synthesized by microorganisms capable to accumulate polyhydroxyalkanoates (PHAs) [1]. The first example of PTEs was a copolymer of 3-hydroxybutyrate and 3-mercaptopropionate, poly(3HB-co-3MP), synthesized by Ralstonia eutropha [2]. The molar fraction of 3MP in these PTEs varied tremendously according to the precursor substrates, cultivation conditions and feeding regimes, considering in particular the preference of the PHA synthase towards 3-hydroxybutyryl coenzyme A, 3HB-CoA [3]. However, due to the consistent presence of acetyl-CoA and thus the continuous supply of 3HB-CoA, R. eutropha did not represent a suitable candidate for biosynthesis of PTE homopolymers. We used a completely different, non-natural PHA biosynthesis system, which has been established in recombinant Escherichia coli. This BPEC pathway comprised a butyrate kinase (Buk) and a phosphotransbutyrylase (Ptb), which genes have been cloned from Clostridium acetobutylicum, and combined them with the PHA synthase (PhaEC) from Thiococcus pfennigii. Employing the engineered E. coli, we synthesized PTE homopolymers consisting exclusively of either 3MP, 3-mercaptobutyrate (3MB) or 3-mercaptovalerate (3MV), respectively [4]. Here, data on the biotechnological production of PTEs in a scale of up to 500 liters including current progress on the upstream and downstream processing will be presented. Furthermore, new insights into the biodegradability of PTEs will be provided. Interestingly, PTEs, which are synthesized by PHA synthases, are not hydrolyzed by PHA depolymerases, as revealed by studies on PHA degrading bacteria as well as by biochemical investigations employing purified enzymes.
論文來(lái)源：International Symposium on Biological Polyesters ,Auguest 22-27, 2004 |
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