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

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