Researchers sequence genome and develop transformation protocol for the alga N. gaditana as a model system for biofuel production
With the goal of transforming a natively robust and oleaginous alga into an improved model system for biofuel production, researchers led by a team from the Colorado School of Mines have sequenced the genome and developed a genetic transformation method for Nannochloropis gaditana CCMP526. The results of their work appear in an open access paper published in the journal Nature Communications.
The team found that with fairly straightforward genetic modification, N. gaditana should be capable of producing biofuel on an industrial scale, and suggested that the continued development of N. gaditana into a model for oleaginous algal biofuel production is a step towards the cost-competitive photoautotrophic production of biofuels.
Photosynthetic algae have long been considered a possible renewable feedstock for biofuel production and have recently experienced intense interest owing to diminishing petroleum reserves and increasing atmospheric levels of CO2. One of the main challenges has been the lack of a genetically tractable model alga capable of industrial biofuels production.
The availability of such an alga could eventually permit the sort of comprehensive systems-biology approaches that have been applied towards the development of highly productive strains of industrial bacteria. The characterization of the genome of N. gaditana and the identification of the genes and pathways that are involved in lipid production in this alga, in combination with the establishment of a method for genetic transformation, allows for further analysis of potential bottle necks in the TAG biosynthesis pathway and the discovery of suitable targets for gene overexpression and/or knockout.—Radakovits et al.
N. gaditana has high photoautotrophic biomass and lipid production rates and can grow to high densities while tolerating a wide range of conditions with regards to pH, temperature and salinity, the team noted. The large majority of lipids in N. gaditana are composed of palmitic and palmitoleic acid with a minor content of myristic and oleic acid, resulting in a relatively simple fatty acid profile. These fatty acids can be used for the production of biodiesel or biogasoline.
N. gaditana is therefore a good candidate for development into a model organism for algal biofuel production, and the availability of a genome sequence and reliable transformation protocols are required advances in this direction.—Radakovits et al.
As part of the work, they investigated the N. gaditana lipid metabolic pathways on the genome and transcriptome levels, quantifying gene transcript levels during a relatively low lipid production stage, (logarithmic growth), and a high lipid production stage, (stationary phase) after nitrate depletion. They also conducted comparative phylogenomic analyses among other algal lineages to determine genes unique to N. gaditana and to identify sets of conserved proteins across photosynthetic stramenopiles (a large algal kingdom).
Although common laboratory model algae, such as C. reinhardtii and P. tricornutum have had transformation protocols available for more than a decade, the relatively low biomass production rates in most of these strains have kept them from becoming industrially relevant, the authors said. While there have been reports of successful genetic transformation of Nannochloropsis oculata, 99% of the transformants lost the transgene after 1.5 months of cultivation, indicating that the majority of the transformants had not truly incorporated the transgene into the genome.
These earlier attempts on N. oculata used foreign promoters or viral promoters and did not utilize antibiotic selection. Radakovits et al. show, for the first time, the successful transformation of N. gaditana through the use of different techniques for genetic engineering. They confirmed successful N. gaditana transformation after 4–5 months of growth.
Our results demonstrate a straightforward approach to the genetic modification of this oleaginous alga, and we anticipate that the ability to further engineer N. gaditana will allow this organism to emerge as an important model species for algal biofuel production.—Radakovits et al.
Radakovits, R. et al. (2012) Draft genome sequence and genetic transformation of the oleaginous alga Nannochloropis gaditana. Nat. Commun. 3:686 doi: 10.1038/ncomms1688