Inoculation with a Rhizobium sp. strain enhances lipid productivity of oleaginous microalgae.

DO NASCIMENTO M; ORTIZ MÁRQUEZ JC; DUBLAN M DE LOS A; CURATTI L

Mar del Plata

Congreso; X Congreso Anual de la Sociedad Argentina de Microbiología General; 2014

Sociedad Argentina de Microbiología General

Increasing demand of food and energy and concerns on environmental decay, represent some of the main current challenges for Humankind. However, what is even more challenging is how to harmonize these three often conflicting interests for sustainable development. The production of biofuels, food, feed and biomaterials from microalgae biomass represent a promising alternative to bring into line all these concerns. Currently, microalgal biomass is produced commercially mostly for high value products. However, biofuels from microalgae are not commercial yet mostly because production costs are still too high. Some of the drawbacks concern to a very high demand of agrochemicals, which also entails some detrimental effect against the environment. The use of plant growth-promoting bacteria (PGPB) is widespread in modern agriculture. However, the potential of growth-promotion of aquatic microalgae by bacteria remains mostly unexplored. This study reports the isolation and identification of cultivable heterotrophic bacteria after 3 years enrichment by serial dilution of monoalgal cultures in mineral medium. We further identified Rhizobium strain 10II as a likely general microalgae-growth promoter. An artificial consortium between Ankistrodesmus sp. and Rhizobium sp. has been characterized in more detail. Upon inoculation with the bacterium, the microalga exhibited increments of up to 50% in chlorophyll, biomass and lipid content of the oleaginous microalgae. The stimulation effect was apparently related to indol-3-acetic acid and/or vitamin B12 produced by the bacterium in exchange for photosynthetic exudates. Inoculated cultures reached a high lipid productivity of up to 112 mg . L -1 . d-1 after optimization. Lipids from the consortium biomass show no difference in fatty acids composition in comparison to axenically-cultivated microalgae. Interestingly, the consortium oil was highly enriched in Ω3 fatty acids, up to 25 % p/p, with a significant proportion of stearidonic acid, suggesting potential as an alternative land-based source of essential fatty acids.