Microalgae have become an increasingly interesting field of research for the production of biofuel and health beneficial lipids such as omega-3. Useful characteristics of the algae are their rapid growth and high levels of lipid accumulation. For growth of microorganisms as biofactories to industrially produce bulk or specialty compounds, economically feasible and energetically efficient feed substrates and conditions are required. Recent developments in electrolysis processes yielding acetate have opened up the possibility of acetate as a future cheap and sustainable carbon source alternative in microalgae cultivations. Several organisms have been reported to grow on acetate as carbon source across prokaryotes and eukaryotes. This thesis demonstrates the mixotrophic growth of microalgae Nannochloropsis oceanica utilizing acetate as a carbon source. For an industrially relevant strain the growth needs to be improved, and this thesis project aims to further enhance the growth on acetate through addition of the bacterial ackA/pta acetate metabolic pathway. The thesis further explores the lipid accumulation in the algae as an effect of acetate. The intensity of light and nitrogen depletion were demonstrated to have a large impact. Moreover, the growth of the yeast Saccharomyces cerevisiae on acetate containing media was confirmed. The attempt to improve acetate metabolism in the yeast through implementing the ackA/pta pathway however resulted in a negative impact on growth and acetate tolerance.