Sustainable CO2 valorization for PHB production towards circular economy: metagenomic insights on enriched indigenous microbial cultures

Abstract

Abstract This study developed resilient mixed microbial cultures (MMCs) from diverse indigenous sources  2 through strategic pretreatment and enrichment, robust conversion of CO 2 and bicarbonate into volatile fatty acids (VFAs) and polyhydroxybutyrate (PHB) was achieved. This article establishes a sustainable biotechnological platform, transforming waste CO 2 into valuable bio-products and biodegradable polymers, thereby bridging a circular bioeconomy approach. In Phase I, CO 2 was converted into VFAs (2.017, 2.307, 3.243, and 3.467 g/L) by anaerobic MMC and PHB (3.2% (0.082 g/L)) by aerobic cultures, respectively.The reduction in pH was observed to 3.45 ± 0.22 due to pretreatment methods, indicated acetogenic dominance. In phase II, VFA was recirculated for PHB production (6.5 ± 0.24%) and molecular confirmation was done using FTIR and NMR.ted The anaerobic MMC achieved a CO 2 reduction efficiency of 70 ± 1.78%, while aerobic cultures showed 45 ± 1.26%, contributing to the production of biodegradable PHB, thus closing loop towards circular bio-economy. This study also shows carbon balance and thermodynamic feasibility of converting CO₂ into PHB via microbial fermentation, highlighting the energy requirements and process efficiency. Metagenomic analysis of microbial consortia, using 16S rRNA (V3-V4) sequencing, identified key bacteria for CO 2 bioconversion. Anaerobic genera like Pseudomonas and Halomonas dominated VFA production, while aerobic bacteria such as Brevundimonas, Achromobacter were predominant in PHB synthesis. KEGG analysis predicts genetic pathways for CO 2 fixation.