Transcriptome analysis ofAurantiochytrium limacinumunder low salt conditions

Aurantiochytrium limacinum can accumulate high amounts of omega-3 polyunsaturated fatty acids, especially docosahexaenoic acid (DHA). Although salinity affects the DHA content, its impact on the metabolic pathway responsible for DHA production in A. limacinum is not completely understood. To address this issue, we investigated the transcriptional profile of A. limacinum under hypoosmotic stress. We first cultured A. limacinum under typical and low salinity for RNA sequencing, respectively. Transcriptome analyses revealed that 933 genes exhibited significant changes in expression under hypoosmotic conditions, of which 81.4% were downregulated. Strikingly, A. limacinum downregulated genes related to polyketide synthesis and fatty acid synthase pathways, while upregulating β-oxidation-related genes. In accordance with this, DHA production significantly decreased under hypoosmotic conditions, while antioxidant-related genes were significantly upregulated. Considering that β-oxidation of fatty acids generates energy and reactive oxygen species (ROS), our results suggest that A. limacinum utilizes fatty acids for energy to survive under hypoosmotic conditions and detoxifies ROS using antioxidant systems.