Lipid-producing Strain Research Articles

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 ± 21 mgTFA (gC)-1 for the wild type (WT) and 269 ± 49 mgTFA (gC)-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 ± 64 mgTFA (gC)-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.

Screening of Lipid High Producing Mutant from Rhodotorula Glutinis by Low Ion Implantation and Study on Lipid Extration Technique

The paper studied on parameters of ion implantation into lipid producing strain Rhodotorula glutinis and lipid extration technology. It was found that the strain had a higher positive mutation rate when the output power was 10keV and the dose of N+ implantation was 80×2.6×1013 ions/cm2. Then a high-yield mutant strain D30 was obtained and it’s lipid yield which was 3.10 g/L increased by 33.05% than that of the original. Additionally, statistically-based experimental designs were applied for the optimization of lipid extraction by acid-heating coupling ultrasonic technique. By a Plackett-Burman design, it was found that three factors, treatment time of HCl (p=0.036) , ultrasonic time (p=0.0105) and rate of extracting solution (VCHCl3:VCH3OH) (p=0.0105), had significant effect on lipid extraction. Subsequently, these significant factors were optimized using response surface methodology (RSM), and the optimized parameters of lipid extraction were as follows: 34 min for treatment time of HCl, 7.5 min for ultrasonic treating time, 1.9:1 for rate of extracting solution (VCHCl3:VCH3OH). Finally the fermentation characteristic of high-yield mutation strain D30 was studied, when fermentation time was 10 d, it’s lipid yield increased to 7.81 g/L

Growth optimization of algae for biodiesel production

Algae are favourable as a biofuel source because of the potential high oil content and fast generation of biomass. However, one of the challenges for this technology is achieving high oil content while maintaining exponential or high growth of the organism. Introducing a two-stage reactor to optimize both growth and oil content of the algae could be a solution to this hurdle. The aim of this study was to determine the reactor design parameters of the first-stage reactor, which would optimize growth of two algal strains, Oocystis sp. and Amphora sp. Growth kinetics were monitored by in vivo fluorescence and correlated to dry mass for both cultures under several environmental conditions during exponential growth. Temperatures of 25 and 30°C and light intensities of 150 and 80 μmol m(-2) s(-1) provided the most robust growth for Oocystis sp. and Amphora sp., respectively. Both strains showed optimized growth at a light : dark cycle of 16 : 08. At these conditions, the doubling rate for Oocystis sp. was 0·333 d(-1) and for Amphora sp. was 0·179 d(-1) . For both cultures, growth rate was more dependent on light : dark cycle and temperature than light intensity. Both strains grew slower in this work than data reported in the literature, however agitation and air/CO(2) sparging were not incorporated in the system under study. The highest doubling rate for Amphora sp. was observed near the maximum tolerable temperature, and it is suggested to grow this strain at 30°C for a consistent high growth rate. Optimized growth conditions were determined for two lipid producing strains identified in the Aquatic Species Program summary report. An optimized, first-stage growth reactor operating at these conditions would thus offer the maximum productivity for an algal biomass feed stream into a lipid-optimized second-stage reactor.

Breeding of high lipid producing strain of Geotrichum robustum by ion beam implantation

To obtain an industrial strain with high lipid yield, the wild strain G0 of Geotrichum robustum was mutated by means of nitrogen ions implantation. Mutagenic effects of strain G0 by low energy N+ ion implantation were studied. The experimental results indicated that the survival rate curve took a “saddle” shape, and the positive mutation rate was increased to 22.00% at the dose of nitrogen ions 2.0 x 1015 ions/cm2 when the survival rate was 28.60%. By repeated screening, a high lipid producing strain G9 was obtained. The biomass, lipid content and lipid yield of the mutant can reach 40.25 g/L, 71.14% and 28.63 g/L after cultured in a 5L fermenter for 8 days, increasing by 52.81%, 68.82% and 157.93% to those of wild strain, respectively. Analysis results on fatty acids composition and relative content by gas chromatography and mass spectrometry showed that the lipid in strain G9 was mainly composed of 16-carbon and 18-carbon fatty acids, including 37.360% oleic acid, 23.631% palmitic acid, 4.458% linoleic acid and 26.465% stearic acid. Such compositional features were quite similar to plant oil. Geotrichum robustum strain G9 may be an ideal high lipid producing strain for biodiesel production