FIG. 5.

Effects of different metal sources on the expression of the S. meliloti sitA promoter. A promoter test plasmid containing a sitA promoter-gusA fusion (pTCC1) was introduced into the S. meliloti wild-type strain Rm1021 (white bars), the S. meliloti fur mutant strain Rm1021Δfur (black bars), and the fur mutant strain Rm1021Δfur complemented with plasmid pTCB1 carrying an intact fur gene (grey bars). The strains were grown in VMM* under the following conditions: (A) no added iron, (B) addition of Fe(III), (C) addition of Fe(II) as the sole iron source. Additionally, Mn(II) was added as indicated. The different strains were grown to an optical density of 0.6 before the assays for glucuronidase activity were carried out. The β-glucuronidase levels are expressed in Miller units, and the error bars indicate the standard deviations. In each case the depicted results were derived from six independent cultures.