It was earlier shown that the mixotrophic cultivation of Synechococcus sp. HS01 in ostrich oil-containing BG11 medium leads to an up to 2.82-fold increase in lipid productivity compared with autotrophic condition. A follow-up investigation was carried out to divulge whether conditions that would increase the lipid content in Synechococcus sp. HS01, bringing about constantly more pool towards the main route for fatty acids synthesis. To this end, the expression patterns of two genes including acc as the main enzyme involved in fatty acid synthesis pathway, converting Acetyl-CoA to Malonyl-CoA and aas gene which convert free fatty acids to active Acyl carrier protein (ACP) (through esterification) were carefully analyzed under different culture conditions. While there is a direct association between the expression of acc gene and changes in lipid content of glucose and acetate-grown cultures, no direct relationship exists between the expression of this gene in ostrich oil-grown culture and nitrogen-deficient conditions. Reduced acc gene expression and increased expression of aas gene in conjunction with increased lipid contents in ostrich oil-grown cultures indicated that exogenous fatty acids can be applied directly to the intracellular lipid synthesis and a possible strategy for achieving greater amount of lipids produced by cyanobacteria. (C) 2018 Elsevier Ltd. All rights reserved.