Genomic and transcriptomic insights into the molecular responses of a biocrust-derived oleaginous microalga sp. WL1 to nitrogen depletion and recovery.

Microalgae surviving in extreme conditions evolve tolerance mechanisms to diverse environmental stresses. Environmental nitrogen limitation or nitrogen starvation poses a significant threat to the growth of microalgae, but it is an effective factor in inducing lipid accumulation in many microalgal species. In this study, we report the genome sequence of a promising oil-producing strain, sp. WL1, which is capable of resisting long-term nitrogen starvation and responds rapidly to nitrogen recovery. Its genome comprises 127 Mb of nuclear DNA and 17,392 protein-coding genes. Comparative genomic and transcriptomic analyses identified a group of genes involved in nitrate metabolism and lipid accumulation. Heterologous expression of three candidate genes in the model cyanobacterium sp. PCC 6803 demonstrated their effects on restoring the cellular chlorophyll upon nitrogen recovery. Our results provide novel insights into the molecular basis of metabolic shifts in response to nitrogen starvation and recovery in microalgae.