Biotechnological valorization of levulinic acid as a non-sugar feedstock: New paradigm in biorefineries.

Due to the severe climate crisis, biorefineries have been highlighted as replacements for fossil fuel-derived refineries. In traditional sugar-based biorefineries, levulinic acid (LA) is a byproduct. Nonetheless, in 2002, the US Department of Energy noted that LA is a significant building block obtained from biomass, and the biorefinery paradigm has shifted from being sugar-based to non-sugar-based. Accordingly, LA is of interest in this review since it can be converted into useful precursors and ultimately can broaden the product spectrum toward more valuable products (e.g., fuels, plastics, and pharmaceuticals), thereby enabling the construction of economically viable biorefineries. This study comprehensively reviews LA production techniques utilizing various bioresources. Recent progress in enzymatic and microbial routes for LA valorization and the LA-derived product spectrum and its versatility are discussed. Finally, challenges and future outlooks for LA-based non-sugar biorefineries are suggested.

Enhancing microbial CO2 electrocatalysis for multicarbon reduction in a wet amine-based catholyte.

Microbial CO2 electroreduction (mCO2ER) offers a promising approach for producing high-value multicarbon reductants from CO2 by combining CO2 fixing microorganisms with conducting materials (i. e., cathodes). However, the solubility and availability of CO2 in an aqueous electrolyte pose significant limitations in this system. This study demonstrates the efficient production of long-chain multicarbon reductants, specifically carotenoids (~C40), within a wet amine-based catholyte medium during mCO2ER. Optimizing the concentration of the biocompatible CO2 absorbent, monoethanolamine (MEA), led to enhanced CO2 fixation in the electroautotroph bacteria. Molecular biological analyses revealed that MEA in the catholyte medium redirected the carbon flux towards carotenoid biosynthesis during mCO2ER. The faradaic efficiency of mCO2ER with MEA for carotenoid production was 4.5-fold higher than that of the control condition. These results suggest the mass transport bottleneck in bioelectrochemical systems could be effectively addressed by MEA-assissted mCO2ER, enabling highly efficient production of valuable products from CO2.

Valorization of CO2 to ß-farnesene in Rhodobacter sphaeroides.

The valorization of CO2 into valuable products is a sustainable strategy to help overcome the climate crisis. In particular, biological conversion is attractive as it can produce long-chain hydrocarbons such as terpenoids. This study reports the high yield of ß-farnesene production from CO2 by expressing heterologous ß-farnesene synthase (FS) into Rhodobacter sphaeroides. To increase the expression of FS, a strong active promoter and a ribosome binding site (RBS) were engineered. Moreover, ß-farnesene production was improved further through the supply of exogenous antioxidants and additional nutrients. Finally, ß-farnesene was produced from CO2 at a titer of 44.53 mg/L and yield of 234.08 mg/g, values that were correspondingly 23 times and 46 times higher than those from the initial production of ß-farnesene. Altogether, the results here suggest that the autotrophic production of ß-farnesene can provide a starting point for achieving a circular carbon economy.