Formulation technology: Macrocystis pyrifera extract is a suitable support/medium for Azospirillum brasilense

Abstract

Sustainable agricultural strategies include the use of inoculants that enhance plant growth (and therefore yield) through the action of living microorganisms. The extract of Macrocystis pyrifera, the largest and fastest growing macroalgal species, could be a suitable alternative as a support medium for the design of such inoculants, since it may ensure the long-term viability of the microorganisms. Moreover, certain physiological and biochemical aspects of this extract may prove beneficial when applied to plants. This study characterized and analyzed Macrocystis pyrifera in terms of its nutritional and hormonal composition and its metabolomic profile. Formulations made with different extract concentrations were evaluated for their impact on the growth, viability and cell survival of inoculant strain Azospirillum brasilense Az39. The results show that the most promising algae extracts (AE) are those formulated at 3 and 30 %. They contain a variety of mineral nutrients, such as magnesium, calcium, phosphorus, ferrum, zinc and boron. They also have a high concentration of organic matter and a high carbon/nitrogen ratio. These nutrients, as well as the production of phytohormones and compounds derived from alginic acid, promoted bacterial growth and viability in bacterium-algae formulations over a period of twenty-eight days. Several hormones were detected in the pure AE, in Az39 grown in NFb, and in the combinations of both (AE + Az39). Although these hormones (gibberellins, auxins and cytokinins) were found in all the samples, pure AE had the highest gibberellin content. Cytokinin production was additive in the formulations. Moreover, recovery of A. brasilense cells was significant in in vitro and in vivo assays on Zea mays seeds. These findings provide evidence in favor of using algae extracts as a renewable bioresource for the design of eco-friendly and effective inoculants.