Preservation of chitinolytic Pantoae agglomerans in a viable form by cellular dried alginate-based carriers

Improved viability of Gram-negative bacteria during freeze-dehydration, storage, and soil inoculation is of crucial importance to their efficient application. The chitinolytic Pantoae (Enterobacter) agglomerans strain IC1270, a potential biocontrol agent of soil-borne plant-pathogenic fungi, was used as a model organism to study the efficacy of freeze-dried alginate-based beads (macrocapsules) as possible carriers for immobilized Gram-negative bacterial cells. These macrocapsules were produced by freeze-dehydration of alginate gel spherical beads, in which different amounts of bacteria, glycerol, and colloidal chitin were entrapped. Subsequent drying produced different unexpected structures, pore-size distributions, and changes in the outer and inner appearance of the resultant dried cellular solid. With increasing glycerol content, the proportion of larger pores increased. These structures can be related to changes in the slow-release properties of the dried beads. The amount of glycerol in the beads differed from that in the alginate solution as a result of leakage during the beads preparation and dehydration. Entrapping 10⁹ cells per bead produced from alginate solution containing 30% glycerol and 1% chitin resulted in improved (in comparison to other studies) survival prospects (95%) during freeze-drying. Moreover, immobilization of the bacterium sharply improved its survival in nonsterile irrigated and dry soils compared to bacteria in a water suspension. The results suggest that optimized conservation of Gram-negative bacteria in dry glycerol-containing alginate-based cellular solids is not only possible but applicable for a variety of uses.