FIG. 4.

Overexpression of RhuI upregulates expression of BhuR. B. avium 4169rif containing either pERM26 (rhuI overexpressing plasmid) or pRK415 (vector control) were cultured in Fe-replete broth (BHI plus 144 μM FeSO₄) or in Fe-stressed broth (BHI plus 100 μM EDDHA). Outer membrane proteins from each strain were resolved on an SDS–8.75% polyacrylamide gel and stained with Coomassie brilliant blue. Each lane was loaded with 8 μg of total protein. The positions (in kilodaltons) of molecular mass standards (M) are shown to the right of the gel. The two forms of the Fe-regulated BhuR outer membrane protein of 4169rif (93 and 91.5 kDa) are denoted by asterisks. Arrows denote the positions of the 74- and 50-kDa outer membrane proteins which are influenced by RhuI overexpression.