Production and storage of Rhizobium leguminosarum cell concentrates for use as inoculants

Recovery of Rhizobium leguminosarum cells by centrifugation after growth in an industrial fermenter was 100‐fold higher when cells were grown on yeast extract (5 g/1) as sole source of carbon and nitrogen when compared with the yields recovered when cells were grown in standard mannitol‐yeast extract medium. Methods of storing concentrated suspensions of R. leguminosarum were investigated. Freeze‐drying caused a marked decrease in viable cell numbers. Viable cell numbers of bacterial concentrates stored in peat decreased steadily from 10 11 ‐10 12 cfu/g to 10 9 cfu/g or less during 26 weeks storage at room temperature or at 4°C. Cell concentrates stored in 40% glycerol at — 20°C maintained viable numbers higher than 10 11 cfu/ml during a 76 week storage period.