CONICET | Buscador de Institutos y Recursos Humanos

Exhaustion of fossil fuels is one of the major world-wide problems. Thus, the production of biodiesel from alternative feedstocks, such as plants and Microalgae, has been attempted as an alternative energy source. It has been demonstrated that oil productivity by several microalgal strains (i.e. Scenedesmus obliquus) is 100-fold higher than that of soy. However, massive production of biodiesel from algae is not commercial yet, mostly because Production costs are still high. We are exploring the possibility of improving the sustainability of microalge culture in mixed consortia with beneficial bacteria, in a similar way as the current trend in modern agriculture to increase the use of plant growth promoting rhizobacteria.Occurrence of Indole-3- acetic acid (IAA), which promotes the growth of algae and other plant organisms have been reported in many algal species. The role of IAA in plants is linked to cell elongation and division, cell differentiation, among others. In vitro studies demonstrated that several algal species respond to synthetic IAA and in S. obliquus auxin biosynthesis is linked to stress conditions. However genomic comparison indicated a large divergence of IAA signaling between plants and unicellular algae. Interestingly, microalgae growth promoting bacteria tend to produce high levels of IAA. Even so, the physiological role of IAA in microalgae remains unknown. Since IAA acts as a signal molecule in microorganisms, it has been proposed that algae IAA production could be involved in the interaction with surrounding bacterial strains. Azospirillum brasilense is a plant-growth-promoting rhizobacteria (PGPR) that enhances growth of many crop plants. This promoting effect is related to the production of IAA, cytokinin, gibberellin, ethylene and also nitric oxide. Plant growth promotion is IAA dependent, since A. brasilense mutant Faj009, with a 90% reduction in IAA production, is impaired in this effect. Incubation of S. obliquus with synthetic auxins resulted in growth inhibition at high concentrations. However, co-inoculation with 1:1, 1:5 or 1:10 (S. obliquus: A. brasilense) cell-ratios produced a slight increase in S. obliquus growth. Conversely, the same experiment conducted with the mutant Faj009, resulted in an inhibition of S. obliquus growth. Moreover, the bacterial population of the mutant strain remained higher than that of the parental strain. Algae cells appeared to produce IAA under every condition assayed, however it was increased when cells were co-inoculated with the bacterium that produce lower levels of the hormone. None of the treatment led to any changes in neither cell size nor morphology. These results suggest that IAA may participate in unicellular algae-bacteria communication that may result in changes in species relative densities in complex consortia. It is anticipated that advancing in these aspects of microalge-bacteria ecology might have implications for extensive culture of microalgae in the field.