Sustainable Resource Recovery via Bioflocculation: Harvesting Chlorella vulgaris MBFJNU-1 with Aspergillus oryzae

Addressing the high cost of harvesting is critical for the industrialization of microalgae. Filamentous fungus-mediated bioflocculation is a sustainable method for microalgae harvesting, and exploring its flocculation mechanism is key to advancing its practical application. This study systematically investigated the potential bioflocculation mechanism of Aspergillus oryzae FSD181214 to harvest Chlorella vulgaris MBFJNU-1. The analysis of the growth characteristics of A. oryzae FSD181214 and the interaction between fungi and algae indicated that the rough hyphal structure, charge neutralization, and hydrophobic interactions collectively contributed to the initiation and progression of bioflocculation. The highly efficient bioflocculant A. oryzae FSD181214 was obtained through medium screening, and its highest efficiency reached 99.1% within 1 h using pellets cultivated in glucose casamino acid (GC) medium. Chemical composition and micromorphological analysis of A. oryzae FSD181214 pellets with different bioflocculation capacities revealed that the α-Glucan content (21.8% of dry biomass) and the rough reticular structure on the mycelial surface were positively correlated with their efficient flocculation. Transcriptomic and metabolomic analyses identified 1394 differentially expressed genes and 344 differentially accumulated metabolites, and showed that the high bioflocculation capacity of A. oryzae FSD181214 was associated with key pathways including glycerophospholipid metabolism, tyrosine metabolism, pentose and glucuronate interconversions, and ABC transporters. Overall, the efficient bioflocculation strategy and the elucidated potential flocculation mechanism together support microalgae harvesting, contributing to sustainable resource recovery from microalgal biomass.