Aerial microalgae Coccomyxa simplex isolated from a low-temperature, low-light environment, and its biofilm growth and lipid accumulation

Abstract

Biofuels produced from renewable resources could be an effective and sustainable alternative to fossil fuels. However, biodiesel production from microalgae is slow during cold periods, which are unfavorable for the growth of conventional microalgae, especially in outdoor mass cultivation. We screened and isolated aerial microalgae that are able to grow at lower temperatures and light intensity than conventional algae. Seven aerial microalgae were isolated from the surface of rocks in a mountainous district in Japan. These microalgae were identified as Coccomyxa simplex (KGU-H002–008 strains), class Trebouxiophyceae, based on 18S rRNA gene analysis. These algal strains were cultured at 15 °C and 15 μmol photons m−2 s−1 until nitrogen was depleted in the liquid culture medium. Their biomass reached 0.7–1.5 g (dry cell weight) per L culture medium. The fatty acid contents of KGU-H002, -H004, and -H005 were approximately 150 mg g−1 dry cell weight (dcw), and these strains produced abundant C16 and C18 fatty acids. We prepared biofilms of C. simplex KGU-H002, -H004, and -H005, and examined their biomass and fatty acid accumulation in the aerial phase at 15 or 25 °C under low light intensity. Under both temperature conditions, the three strains showed a similar increase (~2.2-fold) in biomass. In KGU-H002 and -H004, the fatty acid content was higher at 15 °C than at 25 °C. These results indicate that aerial cultures of C. simplex KGU-H002 and -H004 have potential applications in biodiesel production under low temperature and low light intensity.