Dual-mode cultivation of Chlorella protothecoides applying inter-reactors gas transfer improves microalgae biodiesel production.

Chlorella protothecoides, a lipid-producing microalga, was grown heterotrophically and autotrophically in separate reactors, the off-gases exiting the former being used to aerate the latter. Autotrophic biomass productivity with the two-reactor association, 0.0249gL(-1)h(-1), was 2.2-fold the value obtained in a control autotrophic culture, aerated with ambient air. Fatty acid productivity was 1.7-fold the control value. C. protothecoides heterotrophic biomass productivity was 0.229gL(-1)h(-1). This biomass' fatty acid content was 34.5% (w/w) with a profile suitable for biodiesel production, according to European Standards. The carbon dioxide fixed by the autotrophic biomass was 45mgCO2L(-1)h(-1) in the symbiotic arrangement, 2.1 times the control reactor value. The avoided CO2 atmospheric emission represented 30% of the CO2 produced in the heterotrophic stage, while the released O2 represented 49% of the oxygen demand in that stage. Thus, an increased efficiency in the glucose carbon source use and a higher environmental sustainability were achieved in microalgal biodiesel production using the proposed assembly.

Enhanced lipidic algae biomass production using gas transfer from a fermentative Rhodosporidium toruloides culture to an autotrophic Chlorella protothecoides culture.

In order to produce single-cell oil for biodiesel, a yeast and a microalga were, for the first time, grown in two separate reactors connected by their gas-phases, taking advantage of their complementary nutritional metabolisms, i.e., respiration and photosynthesis. The yeast Rhodosporidium toruloides was used for lipid production, originating a carbon dioxide-enriched outlet gas stream which in turn was used to stimulate the autotrophic growth of Chlorella protothecoides in a vertical-alveolar-panel (VAP) photobioreactor. The microalgal biomass productivity was 0.015 gL(-1)h(-1), and its lipid productivity attained 2.2 mgL(-1)h(-1) when aerated with the outlet gas stream from the yeast fermenter. These values represent an increase of 94% and 87%, respectively, as compared to a control culture aerated with air. The CO2 bio-fixed by the microalgal biomass reached an estimated value of 29 mgL(-1)h(-1) in the VAP receiving the gas stream from the fermenter, a value 1.9 times higher than that measured in the control VAP.

Ethanol-induced dimorphism and lipid composition changes in Mucor fragilis CCMI 142.

AIMS: To study the effect of ethanol on morphology, lipid production and fatty acid profile of Mucor fragilis CCMI 142 cultures. METHODS AND RESULTS: Cell inhibition in shake flask cultures due to alcohol toxicity grew linearly from 0.418 mol x 1(-1) to 0.816 mol x 1(-1) ethanol corresponding to a decrease of specific growth rate. The growth inhibition constant took the value of 2.27 mol x 1(-1). The germination of fungal spores into hyphae is inhibited by concentrations from 0.418 mol x 1(-1) to 0.816 mol x 1(-1) ethanol. In this range, M. fragilis CCMI 142 spores form, exclusively, budding yeast-like cells instead of filaments. Below 0.418 mol 1-1 ethanol the formation of yeast-like cells was stimulated and there was a spore germination delay. CONCLUSION: The lipid content decreased as the concentration of ethanol increased, and was associated with an increase of unsaturated/saturated fatty acid ratio. SIGNIFICANCE AND IMPACT OF THE STUDY: The major conclusion of the study is the production of an enriched unsaturated fatty acids final product with particular emphasis to the presence of gamma-linolenic acid (18:3omega6) a biologically active compound with a useful impact in nutraceutical science.