Derepression of the Azotobacter vinelandii siderophore system, using iron-containing minerals to limit iron repletion

Abstract

A. vinelandii solublilized Fe from certain minerals using only dihydroxybenzoic acid, which appeared to be produced constitutively. Solubilization of Fe from other minerals required dihydroxybenzoic acid and the siderophore N,N''-bis-(2,3-dihydroxybenzoyl)-L-lysine (azotochelin) or these chelators plus the yellow-green fluorescent siderophore azotobactin. In addition to this sequential production of siderophores, cells also demonstrated partial to hyperproduction relative to the Fe limited control. The Fe sources which caused partial derepression of the siderophores caused derepression of all the high MW Fe-repressible outer membrane proteins except a 77,000-MW protein, which appeared to be coordinated with azotobactin production. Increased siderophore production correlated with increased production of outer membrane proteins with MW of 93,000, 85,000 and 77,000, but an 81,000-MW Fe-repressible protein appeared at a constant level despite the degree of derepression. When Fe was readily available, it appeared to complex with a 60,000 MW protein believed to form a surface layer on the A. vinelandii cell.