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

Isomelezitose (IMZ) is of interest as a potential osmoprotectant, but it has not been previously characterised even though the structurally similar trisaccharide melezitose 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 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. BCA cell viability and growth recovery rate after drying and storage at 25 oC were assessed. The data showed that IMZ and impure IMZ reaction products can function similarly to melezitose 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 25 oC in vacuum-sealed bags. Biocontrol treatments with IMZ suppressed disease by 15–35% more thancontrols without any added osmoprotectant. Neither IMZ nor two impure enzyme reaction products impacted germination of dry rot causative Fusarium sambucinum conidia or subsequent hyphal growth under gnotobiotic conditions. For the first time, the osmoprotective capability of IMZ 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.