Discerning promotion mechanisms of fungi Clonostachys rosea on growth of freshwater microalga Chlorella sp. by non-contact culture

Fungi-microalgae consortia have great potential in microalgae harvesting and wastewater treatment. However, the symbiotic mechanisms underlying diffusible signaling metabolite production by fungi and microalgae remain unclear. Here, the positive impacts of Clonostachys rosea on Chlorella sp. were investigated using metabolomics and transcriptomics during a 5-day non-contact co-culture experiment. Co-cultured Chlorella sp. had a significantly higher growth rate and better photosynthetic performance than its mono-culture equivalent. The metabolites played important roles in the up-regulation of energy and amino acid metabolism processes in algal cells, whilst transcriptomics showed the up-regulation of genes involved in photosynthesis and signaling molecules. The biosynthesis of tryptophan and indole-3-acetic acid (IAA) was up-regulated in both algal cells and fungi, indicating that IAA is an important diffusible signaling molecule for algal growth regulation. This work provides novel insights into the signaling molecule interactions between fungi and microalgae in fungi-microalgae consortia.