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 1011-1012 cfu/g to 109 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 1011 cfu/ml during a 76 week storage period.