The dwindling nature of petroleum resources and increased emission of greenhouse gases into the atmosphere have accelerated efforts towards the finding of alternatives to the extensively used petroleum-derived plastics.
Two independent yet intermingled revolutions contribute to a paradigm shift of polymer chemistry from the 20th into the 21st century:
- (1) a switch away from fossil carbon into renewable plant based carbon ( which in turn calls for a process shift from oxidation to reduction ) and
- (2) a shift from thermo-chemical reactions with hydrogen ions and transition metals as catalysts to biochemical reactions with enzymes as catalysts.
The technical paper by Nduko, John Masani; Matsumoto, Ken-ichiro; Taguchi, Seiichi extracted from ACS Symposium Series (2013), 1144 (Green Polymer Chemistry: Biocatalysis and Materials II) gives an example of such a paradigm shift and is summarized below.
Polylactic acids (PLAs), which are produced from renewable biomass, have gained enormous attention as replacements for the conventional synthetic petroleum-derived plastics due to their biodegradability and “bioresorbability”. However, the current system of PLA synthesis involves a two-step bio-chemicals process, where fermentative lactic acid is polymerized using heavy metal catalysts. The remnants of metal catalysts hinder the PLA application for medical devices and potentially for direct contact with some food ingredients.
To circumvent these challenges, bacteria have been engineered to produce lactate (LA)-based polyesters in a single-step metal-free system, which is the focus of this Technical Paper.
- First, the discovery of a lactate-polymerizing enzyme (LPE) that facilitated the creation of a microbial plastic factory (MPF) for the synthesis of LA-based polyesters is discussed in details.
- Then, approaches for the enrichment of LA fraction in LA-based polyesters including the change of culture conditions, the use of metabolically engineered bacteria and further evolution of LPE are described.
- Furthermore, the expansion of monomers that could be copolymerized with LA, the properties of LA-based polyesters, the transfer of the LA-based production system into other bacteria resulting into the synthesis of PLA-like polyesters and the engineering of new LPEs, are highlighted.
- Finally, the future perspectives of the MPF for the synthesis of LA-based polyesters are discussed.
Source : Nduko, John Masani; Matsumoto, Ken-ichiro; Taguchi, Seiichi From ACS Symposium Series (2013), 1144 (Green Polymer Chemistry: Biocatalysis and Materials II), 175-197