Effect of NH₄Cl supplementation on growth, photosynthesis, and triacylglycerol content in Chlamydomonas reinhardtii under mixotrophic cultivation.

This article investigates the effects of ammonium chloride (NH4Cl) supplementation on the growth, biomass, and triglyceride (TAG) content of the green microalga *Chlamydomonas reinhardtii*, focusing on mixotrophic conditions where acetate is supplied as an organic carbon source. The study found that while 25 mM NH4Cl had little impact under photoautotrophic conditions, it reduced microalgal growth but significantly increased TAG accumulation and total lipid content under mixotrophic cultivation, especially in a two-stage cultivation process. Photosynthesis activity was inhibited by NH4Cl after prolonged exposure, although chlorophyll content remained unchanged. Proteomic analysis revealed upregulation of proteins involved in acetate uptake (putative acetate uptake transporter GFY5) and fatty acid metabolism (acyl-coenzyme A oxidase), suggesting that NH4Cl stimulates acetate utilization and lipid biosynthesis pathways. These findings highlight NH4Cl supplementation under mixotrophic conditions as a potential strategy to enhance microalgal lipid production for biofuel applications.