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

This study developed resilient mixed microbial cultures (MMCs) from diverse indigenous sources 2 through strategic pretreatment and enrichment, robust conversion of CO2 and bicarbonate into volatile fatty acids (VFAs) and polyhydroxybutyrate (PHB) was achieved. This article establishes a sustainable biotechnological platform, transforming waste CO2 into valuable bio-products and biodegradable polymers, thereby bridging a circular bioeconomy approach. In Phase I, CO2 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 CO2 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 CO2 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 CO2 fixation.