Drought tolerance of Rhizobium leguminosarum and Rhizobium meliloti

Cell suspension of Rhizobium leguminosarum bv. viciae D-253, R. leguminosarum bv. viciae D-560 and R. melitoti D-557 were incorporated into sterile diatomaceous earth (DE) and dried at room temperature. Initial numbers of colony-forming units (CFU), expressed as log10, were 8.27, 8.36 and 8.51 respectively. After 5 months of storage the CFU numbers were 0.00, 5.99 and 7.43, respectively. R. meliloti D-557 showed only minor lowering of the CFU number even after 16 months of storage (log10 = 7.07). After 7 months of storage in DE some single-colony isolates of D-253 produced 10-100 times higer CFU numbers than the original strain. The isolates of D-560 were much more drought-tolerant. The cells of original strain died after 7 months of storage, log10 of CFU was 6-7 in the isolates. In both strains some of their drought-tolerant isolates had the same specific acetylene-reducing activity of nodule tissue as the original strains. Diatomaceous earth seems to be a prospective carrier for the formulation of becterization preparations.