Flocculation of oleaginous green algae with Mortierella alpina fungi

Microalgae are promising sources of valuable bioproducts such as biofuels, food, and nutraceuticals. However, harvesting microalgae is challenging due to their small size and low biomass concentrations. To address this challenge, bio-flocculation of starchless mutants of Chlamydomonas reinhardtii (sta6/sta7) was investigated with Mortierella alpina, an oleaginous fungus with high concentrations of arachidonic acid (ARA). Triacylglycerides (TAG) reached 85 % of total lipids in sta6 and sta7 through a nitrogen regime. Scanning electron microscopy determined cell-wall attachment and extra polymeric substances (EPS) to be responsible for flocculation. An algal-fungal biomass ratio around 1:1 (three membranes) was optimal for bio-flocculation (80-85 % flocculation efficiency in 24 h). Nitrogen-deprived sta6/sta7 were flocculated with strains of M. alpina (NVP17b, NVP47, and NVP153) with aggregates exhibiting fatty acid profiles similar to C. reinhardtii, with ARA (3-10 % of total fatty acids). This study showcases M. alpina as a strong bio-flocculation candidate for microalgae and advances a mechanistic understanding of algal-fungal interaction.

Automated summary

This study investigates the potential of using the oleaginous fungus Mortierella alpina to bio-flocculate starchless mutants of Chlamydomonas reinhardtii. By adjusting the nitrogen regime, the lipid concentration of triacylglycerides (TAG) reaches 85%. Scanning electron microscopy reveals that cell-wall attachment and extra polymeric substances (EPS) are responsible for algal flocculation. The optimal algal-fungal biomass ratio of 1:1 results in 80-85% flocculation efficiency in 24 hours. Utilizing nutrient-deprived sta6/sta7 mutants and various strains of M. alpina achieves fatty acid profiles similar to C. reinhardtii, including arachidonic acid (ARA).