Effect of Manganese and Zinc Ions on the Growth of Rhizobium

Five strains, representing four species of Rhizobium , were grown in specially purified synthetic culture solutions with manganese or zinc ion concentrations ranging from 0 to 10 −5 m. Omission of Mn 2+ restricted growth to 0.4 to 10% of that of controls, depending on the species. Growth was generally maximum with 10 −6 m Mn 2+ and nearly so with 10 −5 m. Omission of Zn 2+ restricted growth to 1 to 20% of that of controls. Growth was generally maximum with 10 −7 m Zn 2+ . The 10 −5 m level of Zn 2+ was toxic to a variable degree to all species, suppressing the growth of one strain of R. meliloti to 49% of that of controls, and of R. phaseoli to only 0.4% of that of controls. A Mn 2+ × Zn 2+ interaction was also obtained as evidenced by a higher apparent Zn 2+ requirement with 10 −7 m Mn 2+ than with 10 −6 m Mn 2+ .