Electron uptake from solid electrodes promotes the more efficient conversion of CO2 to polyhydroxybutyrate by using Rhodobacter sphaeroides

Abstract

Microbial electrosynthesis (MES) is a promising strategy for the conversion of CO2 to useful chemicals. Nevertheless, the characteristics of electrode-associated cells in MES and their metabolic pathway regulation in CO2 fixation have not been elucidated. This study examined the electrode-driven polyhydroxybutyrate (PHB) production from CO2 in Rhodobacter sphaeroides. The electron uptake and regulation of the metabolic pathways differed in electrode-associated and suspended R. sphaeroides. The electrode-associated cells produced PHB at concentrations up to 23.50 ± 2.8% of the dry cell weight (DCW), whereas the suspended cells grew faster but with a lower cellular PHB content. Gene expression analyses showed that phaA expression was upregulated in electrode-associated R. sphaeroides, whereas phaB expression was downregulated in suspended cells. The electrode-associated cells expressed unconventional CO2 fixation enzymes, such as isocitrate dehydrogenase and formate dehydrogenase, with more PHB synthesis. These results show that CO2 can be upcycled to polymeric substances and provide novel insights into the genetic regulation of electrode-associated cells in MES.