Preservation of Chitinolytic Pantoae agglomerans in a Viable Form by Cellular Dried Alginate‐Based Carriers

Abstract

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 10(9) 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.

Advances in plant growth-promoting bacterial inoculant technology: formulations and practical perspectives (1998–2013)

“…In cases where the biomass of the entrapped bacterial strain is low, a secondary multiplication of the entrapped bacteria in the already-formed beads is required (Bashan 1986a, b). The advantages of alginate formulations are their nontoxic nature, biodegradability, availability at reasonable costs, and slow release of the entrapped microorganisms into the soil that is controled by the polymeric structure (Bashan et al 2002;Zohar-Perez et al 2002).…”

“…Glycerol increases pore size within the beads, which affects the slow release properties, where addition of glycerol and chitin enhanced survival during the freeze-drying process. These beads were able to protect the applied PGPB to the soil compared to bacterial suspension (Zohar-Perez et al 2002).…”

Encapsulation of plant growth‐promoting bacteria in alginate beads enriched with humic acid

“…Several studies thus far have used alginate as the encapsulating material as it forms microbeads instantaneously in presence of polyvalent cations by binding the cation to guluronic acid units (Witter, 1996) in one step with sufficient mechanical strength. Moreover, alginate beads are capable of entrapping sufficient number of bacteria (Fenice et al, 2000;Zohar-Perez et al, 2002). The use of encapsulated cells for environmental applications has several advantages over free cell formulations namely, protection from biotic stresses (Smit et al, 1996) and abiotic stresses such as the inhibitory effect of toxic compounds (Cassidy et al, 1997), enhanced survival and improved physiological activity (Weir et al, 1995), supply of encapsulated nutritional additives (Trevors et al, 1993), increased cell densities and preferential cell growth in various internal aerobic and anaerobic zones of encapsulating gel.…”

Pea Protein Alginate Encapsulated Bacillus subtilis B26, a Plant Biostimulant, Provides Controlled Release and Increased Storage Survival

“…Several studies thus far have used alginate matrix as the encapsulating material since it forms microbeads instantaneously in the presence of polyvalent cations such as calcium [6,8]. Alginate beads have several positive attributes: (i) they are capable of entrapping a sufficient number of bacteria [9]; (ii) they protect the cells by providing a pre-defined and constant microenvironment thus allowing the cells to survive and maintain metabolic activity for extended period of time, and (iii) they provide a controlled release of microroganisms as well as serve as energy source for the microorganisms [10]. Natural polysaccharides and proteins such as starch, malt dextrin, gum Arabic, pectin, chitosan, alginate and legume proteins are widely used for encapsulation of bacterial cells [11,12].…”