Optimisation of the freeze-drying process of Pseudomonas fluorescens strains Pf 153 and CHA0
Within the development of a freeze-drying protocol the freezing process and the drying temperature were optimised for the Pseudomonas fluorescens strains Pf 153 and CHA0. When 21 different protectants were compared, especially sugars protected the vegetative cells during the freezedrying process. After the optimisation of the process the viability before and after freeze-drying of Pf 153 was not significantly different. Therefore, these results demonstrate that the desiccation sensitive P. fluorescens can survive a drying process without loss of viability. Additional storability tests were carried out with the best protectants: skimmed milk, sucrose, glucose, lactose and lignosulfonic acid. The highest viability after storage was obtained when Pf 153 and CHA0 were formulated in lactose. When the efficacy of freshly produced and freeze-dried pseudomonads were compared ad planta, in different plant-pathogen systems, no significant differences were obtained. But, depending on the pathogen, the protectants were influencing the efficacy of the pseudomonads.