Freezing and freeze-drying of the bacteriumRahnella aquatilisBNM 0523: study of protecting agents, rehydration media and freezing temperatures

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Aims:The aim of the present study was to evaluate and compare freezing and freeze-drying treatments for conserving Rahnella aquatilis (BNM 0523) with the goal to achieve an adequate commercial formulation of this biocontrol agent.Methods and Results:The effect of several protective agents, rehydration media and freezing temperatures on the viability and functional activity of the R. aquatilis was investigated. The storage stability at 3 months and 4 years was determined by checking the viability of the cells and their biocontrol capability against Botrytis cinerea by measuring the percentage of reduction of disease severity on apple. The best results were obtained by the freeze-drying of the cells using a mixture of skimmed nonfat milk 10%, yeast extract 0·5% and glucose 1% as the protecting and rehydrating medium, and a quickly freezing (−70°C) before the freeze-drying. In this case, the viability of the cells after 4 years was 98%, and their antagonistic ability showed a little decrease with respect fresh cells.Conclusions:The studies showed that R. aquatilis was resistant to freezing and freeze-drying when it was used a mixture of cryoprotectants and that it was possible to obtain inoculums with high viability and good effectiveness for reduction of decay caused by B. cinerea.Significance and Impact of the study:This study is probably the first report about the resistance of R. aquatilis to freezing and freeze-drying treatments and shows that these operations could be useful for obtaining a commercial formulation of this biocontrol agent.

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