Growth characteristics and fatty acids of the thermotolerant green alga Desmodesmus sp. isolated from a freshwater puddle in Ibaraki, Japan

We investigated the growth, thermotolerance, and fatty acid composition of the green alga Desmodesmus sp., which was isolated from a freshwater puddle in Ibaraki, Japan. Incubation experiments on the isolated strain were performed at a range of temperatures (20-40 & DEG;C) with continuous illumination (110 ismol photons m-2 s-1) and nutrient -replete medium. High specific growth rates of 1.14-1.62 day-1 were observed at 20-35 & DEG;C, but growth rates declined to 0.59 day-1 at 40 & DEG;C. Lipid contents were 13.2%-14.4% (% dry weight) at 20-35 & DEG;C and increased to 21.3% at 40 & DEG;C. Some microalgae are known to regulate membrane fluidity by changing their fatty acid compositions in response to changes in ambient temperature. We found that the major polyunsaturated fatty acid (PUFA; C18:3 w3) of Desmo-desmus sp. was negatively correlated with water temperature. By contrast, no significant relationship was identified between temperature and the ratio of saturated to unsaturated fatty acids. The negative relationship between w3 PUFA composition and temperature was stronger among thermotolerant as opposed to non-thermotolerant microalgae. This suggests that thermotolerant Desmodesmus sp. can grow at high temperatures by altering its fatty acid composition to affect membrane fluidity.