Upcycling atmospheric CO2 to polyhydroxyalkanoates via sequential chemo-biocatalytic processes†

Abstract

The reduction of greenhouse gas emissions and the shift away from petrochemical-derived materials are critical goals in modern industrial development and societal progress. Addressing these intertwined challenges demands innovative and sustainable solutions. Here, we present the first example of synthesizing poly[R-(–)-3-hydroxybutyrate] (PHB) from atmospheric CO₂, utilizing a streamlined and integrated process that combines both chemo- and bio-catalytic conditions. Central to our approach is the development of an immobilized catalytic system that efficiently converts atmospheric CO₂ into sodium formate, establishing a sustainable carbon source for formatotrophic organisms. Through Adaptive Laboratory Evolution (ALE), we enhanced the growth rate of the bacterium Cupriavidus necator H16, enabling it to utilize formic acid and formate as the sole carbon and energy sources. The evolved strain, C. necator ALE26, achieved a 1.8-fold increase in the maximum growth rate (μ_max = 0.25 ± 0.02 h⁻¹), attributed to the loss of the megaplasmid pHG1. Employing the adapted strain, we report the highest PHB production rate in continuous fermentation using C. necator for growth on formate. The development of the different stages (sorption and chemo- and bio-transformation) under compatible conditions that minimize the number of work-up stages demonstrates a major advancement in converting atmospheric CO₂ into valuable biopolymers, thus simultaneously contributing to the reduction of greenhouse gases in the atmosphere and to a circular economy of biobased polymers that diminish fossil fuel dependence.