12-01: A model alga for oil production: Nannochloropsis gaditana draft genome, genetic transformation, and high lipid productivities

The use of algal lipid production for biofuel applications has received significant attention. However, none of the current genetically-tractable model algal species are competitive production strains. Here we present a draft genome sequence and a method for genetic transformation of the marine microalga, Nannochloropsis gaditana CCMP526. Nannochloropsis has highly favorable lipid yields, is currently grown commercially, and is a promising biofuel production organism. The genome assembly includes nuclear (~28 Mb) and organellar genomes, and contains 9,052 gene models. The genes required for glycerolipid biogenesis, inorganic carbon assimilation, and a putative single-cell C₄ like carbon-concentrating mechanism were defined. The differential regulation of gene transcription during nitrogen-limited lipid biosynthesis was detailed via RNAseq. Phylogenomic analysis identified genetic attributes of this organism, including gene expansions and unique stramenopile photosynthesis genes, that may explain the distinguishing photoautotrophic phenotypes observed. Additionally, we have developed a method for nuclear transformation, which coupled to the native ability of Nannochloropsis to undergo homologous recombination will allow for facile genomic modifications. The availability of a genome sequence and transformation methods will facilitate investigations into N. gaditana lipid biosynthesis and permit genetic engineering strategies to further improve this naturally productive algal strain.