Effects of iron(III) analogs on growth and pseudobactin synthesis in a chromiumtolerant Pseudomonas isolate

The growth and siderophore production of a fluorescent Pseudomonas species isolated from soil contaminated with chromium was found to be influenced by the presence of trivalent cations. Overproduction of pseudobactin occurred when the isolate was grown in media containing 1 mM Cr(III) under iron-limited conditions but not when Fe(III) was added at 10 microM. Pseudobactin synthesis was derepressed in iron-limited cultures containing 1 mM Sc(III) or Y(III), examples of group III-B elements. We found that Al(III), Ga(III) or In(III), representative metals from group III-A, repressed synthesis of pseudobactin under iron-deficient conditions. Analogs of Fe(III) were found to inhibit growth of the Pseudomonas isolate in iron-limited media and the trivalent metals listed in order of decreasing toxicity were as follows: Ga greater than In greater than Sc greater than Cr greater than Y greater than Al. The inhibition of growth by 1 mM In(III), Sc(III) and Ga(III) was greater during iron-limited growth than in media containing 10 microM Fe(III). These data show that, although the metal analogs of Fe(III) have similar chemical and physical characteristics, the physiological response of the fluorescent pseudomonad when grown in the presence of these metals varied markedly.