Development of hydrolysable polymers for protection, transport and controlled release of plant growth-promoting microorganisms

Abstract

The global demand for agricultural products is increasing due to the growing population and the challenge of feeding it. To deal with food shortages, fertilizers, pesticides, and insecticides are employed to produce high-yield crops. However, concerns about sustainability and safety have emerged with the use of these products. A proposed ecological solution is the administration (inoculation) of plant growth-promoting bacteria (PGPB), such as Azospirillum species, during the planting period. These bacteria act as biofertilizers and play a crucial role in enhancing plant growth and health. Despite the numerous benefits of using Azospirillum, its inoculation is inefficient due to soil heterogeneity, competition with native microflora, and exposure to agrochemicals. Therefore, this work aims to develop hydrolysable polymers based on polyoxalate (PGOX) that enable the dry storage of these bacteria for extended periods, protect them from adversities after inoculation, and control their release into the soil. Polyoxalate is a polyester with high degradability in an aqueous medium that will allow the formation of pores in the capsules when in contact with soil water. The goal is to produce polyoxalate by polycondensation via a sustainable synthesis route and within the principles of green chemistry, using an oxalate source, an organic acid obtained by the photoreduction of CO2, with glycerol, a byproduct of biodiesel production. The great advantage of this system is that hydrolysis will release glycerol, widely used as a bacterial culture medium, and oxalic acid, which will act as a catalyst for its own hydrolysis, contributing to pore formation. The viability of stored bacteria will be evaluated at different temperatures over different days and months, a critical step to enable large-scale use, allowing the development of a viability kinetics model that will help predict viability for extended storage periods. Additionally, the release kinetics of bacteria after storage will also be evaluated using different amounts of oxalic acid in the formulation to aid in capsule pore formation. This route will allow, using A. brasilense as a model, to constitute a possible investigation system for the protection of other growth-promoting bacteria, nutrient fixers or bioprotectors, providing subsidies for the design of new immobilization and protection systems for inoculants in general.