Cultivation is the most expensive step in the production of biodiesel from microalgae, and substantial research has been devoted to developing more cost-effective cultivation methods. Plant hormones (phytohormones) are chemical messengers that regulate various aspects of growth and development and are typically active at very low concentrations. In this study, we investigated the effect of different phytohormones on microalgal growth and biodiesel production in Chlamydomonas reinhardtii and their potential to lower the overall cost of commercial biofuel production. The results indicated that all five of the tested phytohormones (indole-3-acetic acid, gibberellic acid, kinetin, 1-triacontanol, and abscisic acid) promoted microalgal growth. In particular, hormone treatment increased biomass production by 54 to 69 % relative to the control growth medium (Tris-acetate-phosphate, TAP). Phytohormone treatments also affected microalgal cell morphology but had no effect on the yields of fatty acid methyl esters (FAMEs) as a percent of biomass. We also tested the effect of these phytohormones on microalgal growth in nitrogen-limited media by supplementation in the early stationary phase. Maximum cell densities after addition of phytohormones were higher than in TAP medium, even when the nitrogen source was reduced to 40 % of that in TAP medium. Taken together, our results indicate that phytohormones significantly increased microalgal growth, particularly in nitrogen-limited media, and have potential for use in the development of efficient microalgal cultivation for biofuel production.
As energy and environment have become urgent issues, there has been increasing needs to develop alternative energy source, such as microalgal bio-fuel. In this study, we investigated the growth and lipid contents of microalgae Nannochloris oculata under various environmental conditions for biodiesel production. Our results indicated that biomass productivities of N. oculata were correlated with increasing nitrogen concentrations up to 37.5 ppm. High irradiance using 230-250 μmol/m(2) led to higher biomass yields than low irradiance of 160-180 μmol/m(2). Biomass productivities increased further by manipulating surface to volume ratio (S/V), which in turn enhanced light penetration. Finally, optimal biomass productivities (1.04 g/l day) could be achieved by the supplementation of yeast extract. Lipid contents and fatty acid profiles of N. oculata were affected by the different growth conditions. Lipid contents of N. oculata decreased as nitrogen concentration increased. Lower temperature (15 °C) resulted in higher lipid content than higher temperature (25 °C). Fatty acid profiles of N. oculata indicated that palmitic acid (C16:0) and linoleic acid (C18:2) were the two most abundant fatty acids, but the supplementation of yeast extract increased linolenic acid (C18:3) content. Our results suggested the feasibility of N. oculata for the biodiesel production.
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