BACKGROUND Microalgal lipid overproduction has been achieved greatly by stress treatments, which drastically impede cellular biomass and overall productivity, hence providing the impetus to develop a viable strategy to uncouple lipid enhancement from stress associated growth impairment. RESULTS We designed a sequential strategy in Nannochloropsis oceanica, to enhance cellular biomass and carbon sink by providing optimized bicarbonate source during the growth phase, followed by low-temperature treatment to harness the increased cellular biomass and carbon precursors for lipid hyperaccumulation. Provision of bicarbonate (1.0 g/L) remarkably promoted cellular physiological properties, which in turn enhanced cellular biomass and photosynthetic carbon sink. Subsequent low-temperature treatment (16 degrees C) significantly redirected the carbon flux towards lipogenesis and significantly altered fatty acid composition. The designed strategy resulted in significant enhancement of lipid productivity by 2.9-fold than that of control cells and resulted in lipid accumulation up to 57% of dry cell weight without impeding cellular biomass. Interestingly, the sequential treatment altered fatty acid profile, particularly a 8.8-fold increase in the content of eicosapentaenoic acid with health significance. CONCLUSION Our study exemplifies the feasible strategy to potentiate microalgal biomass, and also to circumvent stress associated growth impairment and consequent algal lipid productivity. (c) 2019 Society of Chemical Industry