A note on some factors affecting the survival of Rhizobium cultures during freeze drying and subsequent storage

Viable counts of Rhizobium before and immediately after freeze drying in sucrose-peptone medium (SPM) showed that neither culture age nor cell concentration affected survival. SPM gave greater protection during drying than either dextran-sucrose-glutamate medium or distilled water. The half-lives of freeze-dried cultures stored at 4°C were estimated using an accelerated storage test and were dependent on both the strain and the suspending medium used. It is recommended that Rhizobium cultures, prepared by the procedures used in the Rothamsted Collection of Rhizobium , should be redried at intervals of 30 years.