Genome-centric analysis reveals the importance of granular activated carbon on quorum sensing and glucose metabolism in anaerobic digestion.

Granular activated carbon (GAC) enhances anaerobic digestion (AD) performance, potentially via biofilm promotion, microbial enrichment, and facilitating direct interspecies electron transfer (DIET). In this work, to investigate the role of GAC, DNA was extracted from sludge in lab-scale digesters (with/without GAC) and GAC biofilm. Genome-resolved analysis revealed GAC established distinct niches enriching Methanothrix and Methanosarcina vacuolata. DIET potential would be indicated by strictly filtered pilA genes with the presence of aromatic amino acids, but not the overall pilA genes. While capable of DIET, Methanothrix primarily utilized the acetoclastic pathway. Methanosarcina vacuolata actively partnered with electroactive bacteria, likely via conductive pili. Enhanced performance with GAC primarily stemmed from increased glucose transport activity and microbial enrichment, not DIET. Mature biofilms during prolonged operation may amplify DIET contributions. Thus, the immediate value of GAC lies in optimizing substrate metabolism and spatial community structuring, with biofilm maturation potentially unlocking greater DIET-mediated efficiency.