Gamma-aminobutyric acid coupled with copper ion stress stimulates lipid production of green microalga Monoraphidium sp. QLY-1 through multiple mechanisms

Induction of copper ion (Cu2+) stress is a method used to increase lipid accumulation in microalgae, but it de-creases cell growth. In this work, the impacts of gamma-aminobutyric acid (GABA) coupled with Cu2+ stress on the biomass and oil yield in Monoraphidium sp. QLY-1 were investigated. Results suggested that the combined treatment of GABA and Cu2+ resulted in a higher lipid content (55.13%) than Cu2+ treatment (48.43%). Furthermore, GABA addition upregulated the levels of lipid-relevant genes, cellular GABA, ethylene (ETH), and antioxidant enzyme activities and alleviated oxidative damage caused by Cu2+ stress. The autophagy-relevant gene atg8 was also upregulated by GABA treatment. Further exploration indicated that cell autophagy induced the lipid content up to 58.09% with GABA and CuV stress treatment. This investigation demonstrates that the coupling strategy can stimulate lipid production and shed light on the underlying mechanisms in lipid biosynthesis, cell autophagy, and stress response of microalgae.