Application of isomelezitose as an osmoprotectant for biological control agent preservation during drying and storage

Authors: Slininger, Patricia - Pat; Cote, Gregory; Shea Andersh, Maureen; Dien, Bruce; Skory, Christopher - Chris

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2020
Publication Date: 10/15/2020
Citation: Slininger, P.J., Cote, G.L., Shea-Andersh, M.A., Dien, B.S., Skory, C.D. 2020. Application of isomelezitose as an osmoprotectant for biological control agent preservation during drying and storage. Biocontrol Science and Technology. 31(2):132-152. https://doi.org/10.1080/09583157.2020.1833307.
DOI: https://doi.org/10.1080/09583157.2020.1833307

Interpretive Summary: Over 80% of fungal strains that cause potato dry rot are now resistant to thiabendazol (TBZ) and there is growing pressure to develop non-azole alternatives. Beneficial bacterial strains are being developed as alternative antifungal biological control agents (BCAs) able to suppress several diseases of potatoes, including Fusarium dry rot, late blight, and pink rot and to inhibit sprouting. Further improved dry storage formulations are needed to preserve BCA shelf-life and to lower costs and expedite use of the BCAs by growers. In this research a new osmoprotective sugar (isomelezitose) was discovered to be more protective of BCA viability during drying and storage than other sugars of similar structure currently used in industry. In earlier research, scientists developed a bioprocess to potentially make this sugar at relatively low cost, which would allow it to be economical for agricultural use. This new technology benefits agriculture by further advancing the feasibility of an antifungal microbial alternative to azole chemicals and by serving as a potential co-product of renewable lignocellulose biorefineries with the effect of boosting the rural economy.

Technical Abstract: Various monosaccharides, disaccharides and trisaccharides are known to protect microorganisms against desiccation stress damage. Such protectants are of interest as formulation ingredients to preserve viable microbial cells in applications such as biological control. Isomelezitose (IMZ) is of interest as a potential osmoprotectant, but it has not been previously characterized even though the structurally similar trisaccharide melezitose (MZ) has been previously shown to have excellent protective qualities. The recent discovery that sucrose can be converted to IMZ during glucansucrase reactions suggests that IMZ might become an economical choice as an osmoprotectant for mass producing microbial inoculants, such as biological control agents (BCAs). Because of this opportunity, its osmoprotective function was explored in this work using two strains of Pseudomonas fluorescens that are BCAs used to control maladies of potatoes stored postharvest. Data on BCA cell viability and growth recovery rate after drying and storage at 25oC were collected which showed that IMZ and impure IMZ reaction products can function similarly to MZ and trehalose to significantly reduce viable cell and activity losses during air drying and storage. Biocontrol treatments formulated with IMZ retained the ability to suppress Fusarium dry rot disease by up to 50 % under severe disease challenge, even after storage 28 d at 25oC in vacuum-sealed Mylar bags. Biocontrol treatments with IMZ suppressed disease by 15 to 35% more than the control BCAs without any added osmoprotectant. Neither IMZ nor two impure enzyme reaction products impacted germination of dry rot causative Fusarium conidia or subsequent hyphal growth under gnotobiotic conditions. For the first time, the osmoprotective capability of isomelezitose has been demonstrated and shown to be potentially superior to others previously reported, including the structurally related compound melezitose and the currently marketed disaccharide trehalose.