Association with an ammonium-excreting bacterium allows diazotrophic culture of a eukaryotic microalga

ORTIZ MÁRQUEZ JC; DO NASCIMENTO M; CURATTI L

Tucuman

Congreso; VII Congreso Anual de la Sociedad Argentina de Microbiología General; 2011

Sociedad Argentina de Microbiología General

Research and development of alternative renewable sources of energy has increased in recent years mainly due to the depletion of fossil fuels and global warming, presumably as a consequence of carbon dioxide accumulation in the atmosphere. Biofuels are carriers of solar energy collected at early stages in the form of biomass.  Microalgae biomass is one of the most promising feedstocks for third generation biofuels mainly because of their relative high rate of oil-rich biomass accumulation per unit of space and time and the possibility of using marginal lands for large scale cultivation. Demonstration-scale projects in developed countries have confirmed the technical feasibility of the approach. However, most of the studies have agreed that the strategy is still not economically competitive using the available microlgae strains and technology according to the current prize of oil and laws for environmental protection. Pioneering projects aimed at exploring native microalgae for desirable properties for biofuels production have started in the most developed countries and have regain enthusiasm during the last years spreading towards as much territory as practical. As a contribution to such a major task, we have started a program for the bioprospection of oleaginous microalgae starting from southeastern Buenos Aires.  At present we have isolated more than thirty strains in monoalgal culture, while more than fifty of them are maintained as axenic isolates. Most of them have been identified by classical taxonomy by morphological characters what has allowed a preliminary identification of strains at the level of genus as Chlorella spp., Scenedesmus spp., Desmodesmus spp., Chlamydomonas spp., Ankistrodesmus spp., Haematococcus spp., Selenastrum spp. Additionally, identification has been complemented by sequencing of a ribosomal intergenic region. This approach show that while some of the strains are identical or very close relatives to strains described in other places, others displayed differences compatible with the isolation of novels strains, what is currently under confirmation. We have used a protocol for a relative high-throughput analysis of neutral lipids accumulation based on the fluorescence of the dye Nile Red what has allowed the identification of the up-till-now most promising strains from our collection. These strains accumulate lipids at more that 30 % (p/p) of dry biomass under high light intensity and nitrogen deficiency as confirmed by gravimetric determination of total and neutral lipids. Some of the selected strains have low to very low doubling times of 5 to 9 h at laboratory conditions, using a diluted mineral medium, what highlights its potential for oil-rich inexpensive-biomass production for next generation biofuels and carbon dioxide sequestration. These results also prompted us to continue exploring the national natural resources searching for novel strains potentially useful for biofuels or other applications of inexpensive biomass