Metabolic engineering of Geobacillus thermoglucosidasius for polymer-grade lactic acid production at high temperature.

The production and application of biodegradable polylactic acid are still severely hindered by the cost of its polymer-grade lactic acid monomers. High-temperature biomanufacturing has emerged as an increasingly attractive approach to enable low-cost and high-efficiency bulk chemical production. In this study, thermophilic Geobacillus thermoglucosidasius was reprogrammed to obtain optically pure l-lactic acid- and d-lactic acid-producing strains, G. thermoglucosidasius GTD17 and GTD7, by using rational metabolic engineering strategies including pathway construction, by-product elimination, and production enhancing. Moreover, semi-rational adaptive evolution was carried out to further improve their lactic acid synthesis performance. The final strains GTD17-55 and GTD7-144 produce 151.1 g/L of l-lactic acid and 153.1 g/L of d-lactic acid at 60 °C, respectively. In consideration of the high temperature, productive performance of these strains is superior compared to the state-of-the-art industrial strains. This study lays the foundation for the low-cost and efficient production of biodegradable plastic polylactic acid.