Hydrogen and methane production using engineered microbes integrated with functional nanomaterials catalyst: A comprehensive review Running Title: Nanomaterial-Enhanced Microbial Bio-fuel Production

The global energy transition toward sustainable systems demands biological hydrogen and methane production as clean alternatives to fossil fuels. This comprehensive review examines recent advances in bio-hydrogen and bio-methane production through the synergistic integration of genetically engineered microorganisms with functional nanomaterial catalysts. We analyze breakthrough studies from 2024–2025 demonstrating how synthetic biology approaches, particularly CRISPR-Cas9-mediated metabolic engineering, coupled with strategically deployed nanomaterials, have revolutionized biofuel production efficiency. Conjugated polymer-bacterial biohybrid systems have achieved hydrogen evolution rates exceeding 3.4 mmol g ⁻¹ h ⁻¹, representing over 30-fold improvements compared to conventional systems. Similarly, nanomaterial supplementation in anaerobic digestion systems has enhanced methane yields by 35–80% depending on nanoparticle composition and concentration. We examine the mechanistic foundations of electron transfer enhancement, metabolic pathway optimization through genome editing, and the catalytic roles of metallic, metal oxide, and carbon-based nanomaterials. Critical challenges including nanomaterial biotoxicity, scale-up limitations, and regulatory frameworks are addressed alongside future research directions. This review provides a comprehensive roadmap for developing commercially viable integrated biological-nanomaterial systems for sustainable energy production, directly contributing to renewable energy advancement and environmental impact mitigation.