Cooperation of rhamnolipid and thermophilic bacteria modifies proteinic structure, microbial community, and metabolic traits for efficient solubilization and acidogenesis of mariculture solid wastes

Anaerobic fermentation combined with thermophilic bacteria (TB) pretreatment is a promising method to realize effective waste management and carbon resource recovery. However, undesirable properties of high-strength mariculture solid wastes (MSW) such as high solids concentration, excessive salinity and poor bioavailability limited the overall solubilization and acidogenic efficiency. This study innovatively introduced rhamnolipid (RL) to alleviate this adverse effect, and unveiled its cooperation with TB on enhancing organic matter dissolution and volatile fatty acids (VFAs) production. The results showed that VFAs yield from pretreated MSW was improved by 9.4-15.1 folds with enriched acetate (81.4%-94.4%) in the TB+RL groups. The co-pretreatment of RL and TB disintegrated substrate structure for efficient release of electron shuttles and biodegradable organics. This was because introducing RL reconstructed solid-liquid interfacial charge and molecular arrangement, improved thermophilic enzyme activity, and reduced apoptosis and necrosis cells of TB. Substrate bioavailability was further improved with proteinic structure shifted from α-helix and β-sheet to random coil and aggregated strands, and amide II and carboxyl groups interacted with RL molecules. These changes induced the selective enrichment of hydrolytic and acidogenic bacteria, and the upregulated expression of encoding genes responsible for transmembrane transport, protein hydrolysis, carbohydrate metabolism and acetate biosynthesis. This study provides a new strategy to overcome the bottlenecks of acidogenesis from high-strengthen organic wastes and deciphers the underlying mechanism.