Sustainable Microbial Biostimulant Production by Integrated Bioreactor Fermentation and Membrane Emulsification

Plant growth-promoting microorganisms represent a sustainable alternative to chemical inputs for improving crop yield and nutritional quality. Their commercialization is limited by the lack of effective formulation technologies and fermentations. In fact, their functionality is related to the implementation of a protective matrix required to enhance microbial survival and application efficiency. To hasten their adoption, the development of advanced formulation technologies that can be easily scaled up, operate under mild conditions, and ensure cell immobilization efficiency and survival is needed. The potential of microbial-based biostimulants can be further promoted by the implementation of sustainable and efficient fermentation processes capable of yielding high concentrations of viable microbial cells. In the present study, membrane emulsification was applied as an advanced encapsulation approach to produce alginate capsules containing Kosakonia pseudosacchari TL13, a promising biofertilizer bacterial strain. Citrus waste biomass was converted into K. pseudosacchari TL13 biomass in a bioreactor fermentation, and the microorganism and the fermentation-derived bioactive compounds were simultaneously encapsulated. Results demonstrated that (i) membrane technology can be used to redesign the conventional encapsulation process based on emulsification with reduced shear stress and high efficiency in terms of formulation quality and microorganism loading and survival, (ii) high concentrations of biomass and added-value products (i.e., exopolysaccharides) can be obtained by using low-cost and easily available food waste, and (iii) the downstream of the process can be simplified by using the whole broth as material for biostimulant production. Overall, the proposed integrated strategy permits providing a sustainable process for microbial-based biostimulant production based on process efficiency and environmental impact.