Synergistic Integration of Engineered Methanogenic Archaea and Biochar for Methane Upcycling to Biodegradable Plastics: A Circular Economy Approach

As the dominant methane elimination mechanism on Earth, the anaerobic oxidation of methane (AOM) presents significant potential for methane-to-chemical conversion biotechnology owing to its exceptional carbon and energy utilization efficiency. However, technological advancement faces critical challenges: the inherent unculturability of native AOM-performing methanotrophic archaea under pure growth conditions and their genetic intractability. To overcome these limitations, this study employed <i>Methanosarcina acetivorans</i>, a genetically tractable methanogenic archaeon capable of reversed methanogenesis-mediated AOM, as an engineered chassis for polyhydroxybutyrate (PHB) bioproduction from methane. Through heterologous pathway engineering, we established a synthetic methanotrophic platform integrating an exogenous PHB biosynthesis module. Furthermore, we developed an innovative extracellular electron transfer system utilizing straw-derived biochar as an electron acceptor. Characterization revealed that Fenton-modified biochar demonstrated superior AOM-enhancing performance, which can be attributed to its enhanced electron-accepting capacity. The optimized system combining engineered <i>M. acetivorans</i> with Fenton-biochar achieved ∼0.20 g/L of PHB titer under methane-fed conditions. Isotopic tracing using ¹³C-labeled methane conclusively demonstrated the incorporation of methane-derived carbon into PHB molecules. The circular economy approach demonstrated here establishes a novel paradigm for greenhouse gas conversion and sustainable chemical manufacturing, with potential applications extending to other value-added bioproducts synthesis from methane.