Long-term storage of bradyrhizobia in sterile water

Abstract

Preservation of strains of bradyrhizobia is an important aspect of legume research and development. Storage of strains of bradyrhizobia in sterile water is an inexpensive and simple method of preservation. This study was conducted to determine if bradyrhizobia strains remained viable after being stored in water for 66 months. Twenty-three bradyrhizobia strains were viable and pure after 66 months of storage in water. Nine Bradyrhizobium japonicum strains that were resistant to antibiotics remained viable and pure after 60 months of storage in water. However, three of the nine antibiotic-resistant strains lost antibiotic resistance after storage as assessed by failure to grow on yeast extract mannitol agar plates containing antibiotics. Maintenance in water should be limited to 48 months, at which time bradyrhizobia strains can be revived in media containing appropriate antibiotics and resuspended in water. These results demonstrated that bradyrhizobia strains can remain viable for at least 66 months of storage in water, but these bacteria may lose traits such as antibiotic resistance if stored too long in sterile water.Key words: bradyrhizobia, storage, water.