Biosynthesis of novel thermoplastic polythioesters by engineered Escherichia coli

Abstract

The development of non-petrochemical sources for the plastics industry continues to progress as large multinationals focus on renewable resources to replace fossil carbon. 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 applications. 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.

Neutral Lipid Bodies in Prokaryotes: Recent Insights into Structure, Formation, and Relationship to Eukaryotic Lipid Depots

“…Almost 150 different hydroxyalkanoic acids have now been described as constituents of PHAs (127). Interestingly, new polythioesters, in which the ester bonds between the building blocks were replaced by thioester bonds, were detected recently (89,90). The terminology for PHAs is based on the chain length of the incorporated hydroxy fatty acids and refers to PHA scl (short chain length [C3 to C5]) and PHA mcl (medium chain length [C6 to C14]).…”

Biosynthesis and Biodegradation of 3-Hydroxypropionate- Containing Polyesters

“…strain 6-19 in the presence of lactate, 4HB, and 3HP or lactate, 4HB, 3HP, and 3HB, respectively, as substrates (Table 1). This process was related to a process previously described by Liu and Steinbüchel (27) and Lütke-Eversloh et al (29).…”

Large-Scale Production of Poly(3-Hydroxyoctanoic Acid) by Pseudomonas putida GPo1 and a Simplified Downstream Process

“…As in the case of PHB synthases, different PHA synthases were cloned and expressed in various prokaryotic organisms (46,47,55,58,67); eukaryotic organisms, such as Saccharomyces cerevisiae (40); insect cells (73); and plants (21,48,53). Recently, the range of polymers synthesized by PHA synthases was extended to polythioesters consisting of 3-mercaptoalkanoates by employing PHA-accumulating bacteria, such as Cupriavidus necator (formerly Ralstonia eutropha), which typically accumulate PHB and other short-chain-length PHA, or engineered Escherichia coli strains and various organic thiochemicals as precursor substrates (42,43). Polythioesters exhibit interesting physical and material properties (37,44), and their homopolymers are not biodegradable (37).…”