Enhancement of neutral lipid productivity in the microalga Isochrysis affinis Galbana (T-Iso) by a mutation-selection procedure

Microalgae offer a high potential for energetic lipid storage as well as high growth rates. They are therefore considered promising candidates for biofuel production, with the selection of high lipid‐producing strains a major objective in projects on the development of this technology. We developed a mutation‐selection method aimed at increasing microalgae neutral lipid productivity. A two step method, based on UVc irradiation followed by flow cytometry selection, was applied to a set of strains that had an initial high lipid content and improvement was assessed by means of Nile‐red fluorescence measurements. The method was first tested on Isochrysis affinis galbana (T‐Iso). Following a first round of mutation‐selection, the total fatty acid content had not increased significantly, being $262\pm 21\,{\rm mgTFA}\,{\rm (gC)}^{- {\rm 1}} $ for the wild type (WT) and $269\pm 49\,{\rm mgTFA}\,{\rm (gC)}^{- {\rm 1}} $ for the selected population (S1M1). Conversely, fatty acid distribution among the lipid classes was affected by the process, resulting in a 20% increase for the fatty acids in the neutral lipids and a 40% decrease in the phospholipids. After a second mutation‐selection step (S2M2), the total fatty acid content reached $409\pm 64\,{\rm mgTFA}\,{\rm (gC)}^{- {\rm 1}} $ with a fatty acid distribution similar to the S1M1 population. Growth rate remained unaffected by the process, resulting in a 80% increase for neutral lipid productivity. Biotechnol. Bioeng. 2012; 109: 2737–2745. © 2012 Wiley Periodicals, Inc. The authors developed a mutation‐selection procedure aimed at increasing microalgae lipid productivity. The method was first tested on the Prymnesiophyceae Isochrysis affinis galbana. Two successive mutation‐selection rounds resulted in an 80% increase for neutral lipid productivity. Additionally, phenotypic traits stability was checked for the mutant populations.