Coculture of Chlorella protothecoides and Coccomyxa subellipsoidea enhances cell growth and lipid accumulation: An effective strategy for biodiesel production

Abstract

Microalgae coculture could resist impurities contamination and fulfill many special biosynthetic processes than microalga monoculture, which might be one of the potential strategies in boosting lipid productivity for biodiesel industrialization. This study explored the possibilities of coculturing of Chlorella protothecoides (CP) and Coccomyxa subellipsoidea (CS) in terms of enhanced cell growth and lipid accumulation. Dual-species coculture with a CP:CS inoculation ratio of 3:7 and a carbon/nitrogen (C/N) ratio of 32 achieved a biomass yield of 6.91 g/L and lipid productivity of 1.07 g/L/d, respectively, representing 1.41- to 1.70- and 3.05- to 3.10-fold increases over the values from dual species monoculture. This dual-species consortium also had increased proportions of C16–C18 (>96 %) and C18:1 fatty acid (50.27 %), providing excellent feedstock for biodiesel production. Furthermore, the CP and CS coculture had a shorter 4-day logarithmic growth cycle than either the CP (5-day) or CS (6-day) monoculture alone. Transcriptomic and metabolomic data indicated that CP and CS in dual-species consortium each performed specific tasks: CP increased the carbon sink and decreased lipid β-oxidation, while CS secreted beneficial factors to the extracellular environment to resist contamination with pathogens and stabilize pH fluctuations, thus supporting lipid accumulation. Exogenous metabolite melatonin (50 μM) supplementation further promoted the biomass and lipid content of coculture CP and CS to reach 9.27 g/L and 69.86 %. This mutualistic interaction strategy involving the use of CP and CS to boost lipid productivity could promote development in the industrial field of biodiesel production.