Bioprospecting of microalgae from agricultural fields and developing consortia for sustainable agriculture

Bioinoculation of soil with microalgae, such as cyanobacteria and green microalgae has been identified as an innovative approach to promote sustainable agriculture. In this study, indigenous nitrogen-fixing cyanobacteria and non-nitrogen-fixing green microalgae were isolated from agricultural fields and analyzed for metabolites of agricultural significance for the development of suitable microalgal consortia under nitrogen-deficient conditions. The amount of indole acetic acid (IAA) in biomass extracts from cyanobacteria Calothrix sp. (2.54 ng g-1) and Nostoc sp. (1.52 ng g-1) was significantly higher than in extracts from green microalgae (Chlorella sp. (0.32 ng g-1) and Desmodesmus armatus (0.20 ng g-1). A completely randomized design was used to develop and evaluate eight microalgal consortia on a nitrogen-deficient medium with the selected microalgal strains. The microalgal consortium with superior biomass productivity was evaluated for the production of exopolymers, phytohormones, macronutrients, and micronutrients. A significant improvement in the production of IAA was observed in the consortium compared to the individual isolates, with the highest production of 21.06 ng g-1 occurring in the late log phase. The selected microalgal consortium was further analyzed for biostimulant properties using seed germination assay in Capsicum annuum. A significant increase in seedling length and leaf number was observed in seeds treated with biomass extracts of microalgae consortium compared to the control. The present study paved the basis for developing cyanobacteria and green microalgae-based consortia for agricultural applications.