The Use of Probiotic Bacteria as an Alternative to Enhance or Extend the Metabolic Capabilities of Microalgae

DO NASCIMENTO M; ORTIZ-MARQUEZ J.F.C.; CURATTI L.

Toronto

Congreso; 3rd International conference on algal biomass, biofuels and bioproducts; 2013

We have assembled a collection of microalgae native to south-eastern Buenos Aires, Argentina, a region of the world not-previously bioprospected towards research on biofuels. Some strains presented desirable traits as biodiesel feedstock such as doubling-times of 6 h, lipids accumulation of up to 43 % of their dry biomass, high ratio of mono-unsaturated to poly-unsaturated fatty acids and complete sedimentation in 4h. In parallel, more than fifty fresh water samples were subcultivated by 1:50 dilution in fresh medium lacking any source of carbon and/or energy for heterotrophic bacteria other than microalgae exudates, at fifteen days intervals for two- to three-years. Bacterial strains that could not be removed out of the microalgae cultures by exhaustive dilution were isolated and identified. After a preliminary screening the most reactive isolates (either beneficial or detrimental to microlgae) were strains of Herbaspirillum sp., Rhizobium sp/Agrobacterium sp.,Bosea sp., Xanthomonas sp. , Sphyngomonas sp. and Mycobacterium sp., suggesting a common trend of these bacterial species to engage in interactions with either plants or microalgae. The interaction between an Ankistrodesmus sp. and a Rhizobium /Agrobacterium sp was characterized in more detail. Inoculation with the bacterium produced a nearly two-fold increase in chlorophyll content and cell number. A series of assays suggested that the effect could be mediated by indol acetic acid produced by the bacterium. Growth-promotion of diverse eukaryotic microlgae was also achieved by inoculation with a genetically-modified diazotrophic bacteria that excretes ammonium into the culture medium. The synthetic consortium produced oil-rich biomass using both carbon and nitrogen form the air. We propose artificial symbiosis with selected heterotrophic bacteria, powered by microalgae photosynthetic exudates, may be considered as an alternative strategy to traditional genetic engineering to add or enhance metabolic capabilities of microalage to improve biomass production, low-N-intensive cultivation or other traits. CONICET, ANPCyT, FIBA.