Structure of Dried Cellular Alginate Matrix Containing Fillers Provides Extra Protection for Microorganisms against UVC Radiation

Abstract

Soil microorganisms in general and biocontrol agents in particular are very sensitive to UV light. The packaging of biocontrol microorganisms into cellular solids has been developed as a means of reducing loss caused by exposure to environmental UV radiation. The bacterial and fungal biocontrol agents Pantoea agglomerans and Trichoderma harzianum were immobilized in freeze-dried alginate beads containing fillers and subjected to 254 nm UV radiation (UVC). Immobilization of cells in freeze-dried alginate-glycerol beads resulted in greater survival after UV irradiation than for a free cell suspension. Adding chitin, bentonite or kaolin as fillers to the alginate-glycerol formulation significantly increased bacterial survival. Immobilization in alginate-glycerol-kaolin beads resulted in the highest levels of survival. The transmissive properties of the dried hydrocolloid cellular solid had a major influence on the amount of protection by the cell carrier. Dried alginate matrix (control) transmitted an average of 7.2% of the radiation. Filler incorporation into the matrix significantly reduced UV transmission: Alginate with kaolin, bentonite and chitin transmitted an average of 0.15, 0.38 and 3.4% of the radiation, respectively. In addition, the filler inclusion had a considerable effect on the bead's average wall thickness, resulting in a approximately 1.5- to threefold increase relative to beads based solely on alginate. These results suggest that the degree of protection of entrapped microorganisms against UVC radiation is determined by the UV-transmission properties of the dried matrix and the cellular solid's structure. It is concluded that for maximum protection against UV-radiation-induced cell loss, biocontrol microorganisms should be immobilized in alginate-glycerol beads containing kaolin.

UV protectants for the biopesticide based on Bacillus sphaericus Neide and their role in protecting the binary toxins from UV radiation

“…The formulation prepared from alginate-encapsulated B. thuringiensis var. israelensis and immobilization of bacterial cells in alginate-glycerol-kaolin beads enhances the stability of both spores and toxin against pH, temperature variations, and UV irradiation (Elcin, 1995;Zohar-Perez et al, 2003;Prabakaran and Hoti, 2008). Alternatively, addition of benzaldehyde, methylene blue, yeast extract and cinnamaldehyde to spores of different strains of B. sphaericus showed good protection to UV-C radiation for 240 min exposure (Cokmus et al, 2000).…”

A review on plant growth promoting rhizobacteria acting as bioinoculants and their biological approach towards the production of sustainable agriculture

“…-dried alginate-glycerol beads significantly increased bacterial survival also under UV light radiation (Zohar -Perez et al, 2003). Intraradical structures of G. intraradices embedded in alginate beads were still infective after up to 62 months after storage in plastic vials at 4°C (Plenchette and Strullu, 2003).…”

Probiotic Biofilms

“…Immobilization in several substances provides to the microorganisms several advantages over free-living microorganisms. These advantages include: (i) a continuous source of nutrients without competition with other microorganisms [116] and (ii) protection against environmental stress [66,117], bacteriophages, toxins, and UV irradiation [118]. A recently developed treatment for tertiary domestic wastewaters uses the green microalga Chlorella spp.…”