High shelf-life formulations for Methylobacterium extorquens DSM 21961,a microbial inoculant to enhance strawberry flavour

Abstract: Methylobacterium extorquens DSM 21961 is a promising flavour enhancing agent onstrawberries. For the use as microbial inoculant, a method to produce and formulate thebacterium into a product with high-cell-densities and a long shelf-life is essential. We tested threedifferent growing media and four formulation procedures: (i) a lyophilisate, (ii) a formulation in axanthan matrix, (iii) an encapsulation in alginate with and (iv) without adaptation of the cells tostorage conditions. After storage at six different temperatures and according to the calculateddisintegration kinetics, the xanthan formulation as well as the adapted alginate formulationshowed the best shelf-life. Strawberry plants were treated with these Methylobacteriumformulations, but no statistically significant differences according to cell numbers on leaves wereobserved: DSM 21961 was shown to be established at a level of log10 6.0 cells g-1 leavesmonitored by strain-specific real-time PCR. Comparing all criteria (shelf-life, practicability, plantcolonization, effect, expenses), the xanthan formulation can be suggested as optimal formulationprocedure. For special applications like soil treatments, the alginate beads or the lyophylisate areappropriate formulations. Results open the way for the use of methylobacteria in agriculture.