Encapsulation of Plant Growth-Promoting Bacteria in Poly(itaconic acid) Microspheres by Spray Drying

Abstract

Poly(itaconic acid) (PIA) is a renewable, biobased, hydrophilic polymer of superabsorbent properties, with the potential to replace synthetic superabsorbent polymers in agricultural applications. Herein, we tested PIA for encapsulation of two model plant growth-promoting bacteria (PGPB), Bacillus subtilis and Pseudomonas fluorescens, using spray drying. Linear PIA was prepared, mixed with PGPB, and spray-dried to form microbe-loaded microspheres. The latter were analyzed for mass yield, moisture content, morphology, and microbial survival. Incubation of the microbes with PIA prior to spray drying showed no significant toxicity. The spray-dried microcapsules were about 1-10 μm in diameter, had a moisture content of about 11%, and contained a viable load of microbes (up to 1 × 108 cells/gram of product). The microspheres underwent instantaneous swelling-dissolution to release live bacteria. The CFU data showed a survival of about 79% for B. subtilis after spray drying. This work presents PIA as a safe, sustainable, and promising new encapsulation material for microbial inoculants.