New insights into fungi-mediated flocculation of Chlorella vulgaris: A transcriptomics - metabolomics integration from biosynthesis to mechanism.

Despite fungi-mediated bioflocculation being a promising strategy for efficient Chlorella vulgaris (C. vulgaris) harvesting, the underlying mechanisms remain largely unexplored. In this research, a high-performance flocculating fungi strain, Alternaria alternata J-28 was isolated from wastewater treatment plants (WWTPs). The flocculation performance and properties were assessed. The flocculants and flocculation mechanisms were explored by metabolomics and transcriptomics. The findings indicated that Alternaria alternata J-28, a strain of indigenous fungi from WWTPs could not only harvest C.vulgaris with an efficiency of up to 97 % within just 30 min but also facilitated the growth of C. vulgaris. The porous network mycelium was found to promote C. vulgaris flocculation, while the secreted flocculants such as N-Acetyl-D-Phenylalanine, N-Acetyl-L-Tyrosine, and N-Acetyl-D-Tryptophan were identified for the first time. The synthesis of these flocculants was influenced by several KEGG pathways such as signal transduction, amino acid metabolism, and membrane transport. Alternaria alternata J-28 flocculated C. vulgaris by secreting natural flocculants, supplementing the gap in the flocculation mechanism and contributing to the C. vulgaris harvest for microalgae resource utilization.