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Biosynthesis of novel thermoplastic polythioesters by engineered Escherichia coli


The development of non-petrochemical sources for the plastics industry continues to progress as large multinationals focus on renewable resources to replace fossil carbon1. Many bacteria are known to accumulate polyoxoesters as water-insoluble granules in the cytoplasm. The thermoplastic and/or elastomeric behaviour of these biodegradable polymers holds promise for the development of various technological applications2,3. Here, we report the synthesis and characterization of microbial polythioesters (PTEs), a novel class of biopolymers of general technological relevance. Biosynthesis of PTE homopolymers was achieved using a recombinant strain of Escherichia coli that expressed a non-natural pathway consisting of a butyrate kinase, a phosphotransbutyrylase, and a PHA synthase. Different homopolymers were produced, consisting of either 3-mercaptopropionate, 3-mercaptobutyrate, or 3-mercaptovalerate repeating units, if the respective mercaptoalkanoic acids were provided as precursor substrates to the fermentative process. The PTEs contributed up to 30% (w/w) of the cellular dry weight and were identified as hydrophobic inclusions in the cytoplasm. The chemical and stereochemical homogeneity of the purified PTEs were identified by different methods, and the estimated physical properties were compared to the oxypolyester equivalents, revealing low crystalline order and, for the poly(3-mercaptopropionate) improved thermal stability. The ability to produce PTEs through a biosynthetic route opens up new avenues in the field of biomaterials.

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Figure 1: Metabolic pathways for the biosynthesis of PTEs.
Figure 2
Figure 3: 13C-CP/MAS-NMR spectra of different purification steps of PMP isolated from cells of E. coli JM109 pBPP1.


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We thank Ursula Malkus for expert electron microscopic preparation of the specimens and for taking the TEM micrographs, and Gudrun Kiefermann (Institut für Medizinische Physik und Biophysik, WWU Münster) for photographic work. Further spectroscopic analysis of PTE samples by Heinrich Luftmann and Klaus Bergander (Institut für Organische Chemie, WWU Münster) is gratefully acknowledged. Paul Xia performed the 13C high-resolution NMR experiments.

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Correspondence to Alexander Steinbüchel.

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Lütke-Eversloh, T., Fischer, A., Remminghorst, U. et al. Biosynthesis of novel thermoplastic polythioesters by engineered Escherichia coli. Nature Mater 1, 236–240 (2002).

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