Enzymatic and whole-cell synthesis of lactate-containing polyesters: toward the complete biological production of polylactate

The importance of polylactic acid, a representative bio-based polyester, has been established on a worldwide scale in response to emerging global environmental problems such as green house gas emission and limited petroleum consumption. The current methods for generating this bio-based polymer involve biological synthesis and lactic acid (LA) fermentation, followed by chemical ring-opening polymerization. Among the research community working on polyhydroxyalkanoate polyesters, the prospect of direct biological synthesis of LA into a polymeric form is very attractive from the academic and industrial perspectives. In 2008, this challenge was met for the first time by the discovery of an LA-polymerizing enzyme. Using this novel enzyme, the metabolic engineering approach outlined here provided an entirely new, single organism generation of the polymer. This is a major breakthrough in the field. In this review, we provide an overview of the whole-cell synthesis of LA-containing polyesters in comparison with conventional lipase-catalyzed polymer synthesis in terms of both the concepts and strategies of their synthetic processes.