Lipid productivity and cell wall ultrastructure of six strains of Nannochloropsis: Implications for biofuel production and downstream processing

Microalgae are generating considerable interest for third generation biodiesel production. However, appropriate strain selection is proving challenging due to the significant variation in cellular physiology, metabolic potential and genetics observed even amongst strains deemed morphologically similar. Six strains of Nannochloropsis from the CCAP culture collection were assessed for their lipid productivity and cellular structure, as proxies for oil production and harvesting ease, to assess their suitability as biodiesel production platforms. Differences in growth rate and lipid accumulation across the strains were observed. Nannochloropsis oculata strain 849/7 showed significantly reduced doubling time compared to Nannochloropsis salina strain 849/3, whilst Nannochloropsis oceanica 849/10 produced the highest lipid content. In addition the six strains could be differentiated into 3 distinct classes based on their cell wall thickness, which varied across the strains from 63 to 119 nm and which is independent of both species and geographical isolation location. The importance of these variations in ultrastructure and physiology for biodiesel production is discussed.

Growth dependent silencing and resetting of DGA1 transgene in Nannochloropsis salina

Here we report recombinant expression and activity of the Saccharomyces cerevisiae type 2 diacylglycerol acyltransferase DGA1 functioning in parallel with the native Nannochloropsis salina genes. Expression of DGA1 shifted the chain length distribution of fatty acids produced and reflected an oleoyl-CoA substrate preference. Effect on the total FAME content was moderate and elevated by a maximum of 38%. Expression of the DGA1 transgene varied throughout the culture life cycle and evidence of growth dependent environmental silencing of the transgene was observed. This is to our knowledge the first example of silencing and subsequent resetting in a transgenic microalga. Results from this study add valuable insights into the efficacy of algal genetic engineering and use of these microorganisms as bio-platforms for chemical manufacture.

Growth dependent silencing and resetting of DGA1 transgene in Nannochloropsis salina

Here we report recombinant expression and activity of the Saccharomyces cerevisiae type 2 diacylglycerol acyltransferase DGA1 functioning in parallel with the native Nannochloropsis salina genes. Expression of DGA1 shifted the chain length distribution of fatty acids produced and reflected an oleoyl-CoA substrate preference. Effect on the total FAME content was moderate and elevated by a maximum of 38%. Expression of the DGA1 transgene varied throughout the culture life cycle and evidence of growth dependent environmental silencing of the transgene was observed. This is to our knowledge the first example of silencing and subsequent resetting in a transgenic microalga. Results from this study add valuable insights into the efficacy of algal genetic engineering and use of these microorganisms as bio-platforms for chemical manufacture.

Altered Lipid Accumulation in Nannochlropsis Salina CCAP849/3 Following EMS and UV Induced Mutagenesis

Microalgae have potential as a chemical feed stock in a range of industrial applications. Nannochloropsis salina was subject to EMS mutagenesis and the highest lipid containing cells selected using fluorescence-activated cell sorting. Assessment of growth, lipid content and fatty acid composition identified mutant strains displaying a range of altered traits including changes in the PUFA content and a total FAME increase of up to 156% that of the wild type strain. Combined with a reduction in growth this demonstrated a productivity increase of up to 76%. Following UV mutagenesis, lipid accumulation of the mutant cultures was elevated to more than 3 fold that of the wild type strain, however reduced growth rates resulted in a reduction in overall productivity. Changes observed are indicative of alterations to the regulation of the omega 6 Kennedy pathway. The importance of these variations in physiology for industrial applications such as biofuel production is discussed.