TABLE 2.

Effect of Mn²⁺ and Fe³⁺ in siderophore production of S. meliloti wild-type strains and fur mutants

S. meliloti strain	Mean rhizobactin 1021 concn ± SD (nM) of cultures grown ina:
	M3Fe50	M3	M3Mn50	M3E100	M3E100Mn50
1021	22 ± 1	61 ± 6	58 ± 4	120 ± 24	144 ± 32
Mf1	24 ± 8	78 ± 8	68 ± 9	135 ± 30	106 ± 18
242	33 ± 4	109 ± 10	95 ± 10	173 ± 18	132 ± 30
Mf2	26 ± 1	94 ± 10	70 ± 20	160 ± 42	160 ± 38

^aConcentration of rhizobactin 1021 in the supernatant was estimated under the assumption that 1 mol of the trihydroxamate deferoxamine mesylate is equivalent to 1.5 mol of the dihydroxamate rhizobactin 1021. Results were normalized to an optical density of 1. The data shown are based on three separate experiments.