Ability of Agrobacterium tumefaciens and A. rhizogenes strains, inability of A. vitis and A. rubi strains to adapt to salt-insufficient environment, and taxonomic significance of a simple salt requirement test in the pathogenic Agrobacterium species

Resistance to a 1% or higher concentration of NaCl is an important trait for taxonomic discrimination of species in the family Rhizobiaceae. However, we have little knowledge about how much salt rhizobia require. In this study, we examined the requirement of NaCl for growth in relation to the NaCl sensitivity in the pathogenic Agrobacterium species. Consistent with the previous salt resistance data, the standard Luria Bertani medium containing 0.5% NaCl (LB) permitted A. tumefaciens and A. vitis strains to grow well, but not A. rhizogenes strains. In contrast, LB lacking NaCl (LB-NaCl) allowed the A. rhizogenes and A. tumefaciens strains to grow well but not the A. vitis strains. In LB-NaCl, viability of A. vitis strains decreased 500-fold in 24 h. The addition of KCl, MgCl2 or MgSO4 to LB-NaCl restored the growth of A. vitis strains. These data indicate higher salt requirements in A. vitis than those in A. tumefaciens and A. rhizogenes and adaptability of A. tumefaciens to salt-insufficient environments. An A. rubi strain was salt dependent like A. vitis. The experiment was extended to strains in related genera. Checking growth on the two media was very easy, gave a new trait and clear results, and thereby proved useful as an additional method for taxonomic identification.