# An Efficient CO2‐Upcycling Platform Based on Engineered Halomonas TD with Enhanced Acetate‐Utilizing Capacity via Adaptive Laboratory Evolution

## TL;DR

Scientists engineered a salt-resistant bacterium to efficiently convert CO2-derived chemicals into valuable products like bioplastics and antioxidants, offering a promising solution for carbon capture and utilization.

## Contribution

The study introduces an engineered Halomonas TD strain (TD80) with enhanced acetate utilization and high carbon conversion rates for CO2 upcycling.

## Key findings

- TD80 achieved 26.0 g L−1 ectoine and 29.6 g L−1 PHB in fed-batch studies.
- A non-canonical pathway increased PHB content from 60 wt% to 80 wt%.
- Co-producing ectoine and PHB boosted carbon conversion rate to 53.7 mol%.

## Abstract

Biohybrid conversion of carbon dioxide (CO2) into value‐added bioproducts via engineered microbes using CO2‐derived electrolytes (CDE) addresses global CO2 emissions, but most recombinants have poor saline CDE tolerance and low carbon conversion rate (CCR). Herein, Halomonas TD (salt‐resistant) was adaptively evolved into TD80, which efficiently uses acetate; its aceE gene mutation (encoding pyruvate dehydrogenase) drives acetate utilization. Subsequently, different biosynthesis pathways in TD80 enabled high yields of poly‐3‐hydroxybutyrate (PHB), poly‐3‐hydroxybutyrate‐co‐4‐hydroxybutyrate (P34HB), 3‐hydroxybutyrate (3HB), violacein, ectoine, 1,3‐diaminopropane (1,3‐DAP) and superoxide dismutase (SOD), respectively. Moreover, 26.0 g L−1 ectoine and 29.6 g L−1 PHB can be achieved by recombinant TD80 strains during fed‐batch studies. Finally, a non‐canonical pathway was designed to recycle the excess malonyl‐CoA into PHB. The resultant PHB content in fed‐batch study was increased from 60 wt% to 80 wt%. Moreover, co‐producing ectoine and PHB could further boost the CCR of CDE‐to‐product up to 53.7 mol%, which exemplified promising potential for biohybrid CO2 upcycling involved in carbon capture and utilization system. Furthermore, TD80 was engineered to grow on formate only aiming to achieve the full use of CDE. The establishment of technology and economy assessment (TEA) confirmed the Halomonas‐based platform’s efficiency and economic viability for carbon footprint reduction.

An electrochemical system is designed to convert CO2 into CO2‐derived electrolytes (CDE), mainly containing acetate and formate. The underlying mechanism of acetate metabolism in Halomonas TD80 is explored via ALE. Engineered TD80 produced high‐yield diversified products from CDE. Furthermore, TD80 is engineered to utilize formate for PHB synthesis by the rGly pathway, demonstrating strong potential for full utilization of CDE in the future.