Desmodesmus

Abstract: Cultivation of microalgae in wastewater could significantly contribute to wastewater treatment, biodiesel production, and thus the transition to renewable energy. However, more information on effects of environmental factors, including light intensity, on their growth and composition (particularly fatty acid contents) is required. Therefore, we investigated the biomass and fatty acid production of four microalgal species, isolated in the Northern hemisphere and grown at three light intensities (50, 150 and 300 μE m−2 s−1). Increases in light intensities resulted in higher biomass of all four species and, importantly, raised fatty acid contents of both Desmodesmus sp. and Scenedesmus obliquus. Fourier-transform IR spectrometry analysis showed that the increases in fatty acid content were associated with reductions in protein, but not carbohydrate, contents. Assessment of fatty acid composition revealed that increasing light intensity led to higher and lower contents of oleic (18:1) and linolenic (18:3) acids, respectively. The microalgae consumed more than 75% of the nitrogen and phosphorus present in the wastewater used as growth medium. The results show the importance of optimizing light intensities to improve fatty acid production by microalgae and their quality as sources of biodiesel. In addition, increase in fatty acid content is associated with decrease in protein content.

Abstract: Organisms belonging to the green algal genera Desmodesmus and Scenedesmus are characterized by a high degree of flexibility allowing them to be true cosmopolitans and to withstand harsh conditions. The environmental conditions determine which phenotypes are being produced and one of the most dangerous situations for the algae is when the organisms are confronted with strong grazing pressure from numerous zooplankton organisms. An overview is given of several aspect of an induced defense in many non-spiny Scenedesmus and some spiny Desmodesmus that may form typical protective eight-celled colonies to avoid mortality from numerous grazers. The morphological response does seem to be linked with a herbivorous zooplankton chemical cue, rather than to a more general animal excretory product. The grazing activity of small sized grazers is reduced, but not of large Daphnia. However, arguments are given why grazing protection of colonial Scenedesmus is probably more efficient under natural than under carbon/light limited laboratory conditions. Finally, a life-history cycle of Desmodesmus and Scenedesmus is presented in which biological aspects such as the anti-grazer response and sexual reproduction are being included.