Siderophore-Dependent and -Independent Iron Acquisition Pathways in Marinobacter Nauticus SP17

We explored the iron acquisition pathways of Marinobacter nauticus SP17, which exhibits distinct growth modes, manifesting as a planktonic population on acetate and forming a biofilm while utilising n-alkanes or triglycerides as substrates. The expression of genes encoding iron-containing proteins and growth yields measured under varying iron concentrations suggest that the balance between iron demand and availability plays a key role in regulating these genes in response to the carbon source and/or growth mode. Phenotypic studies of a petrobactin-deficient mutant revealed that, although this siderophore is important, it is not essential for growth on all substrates under iron-deplete conditions. This suggests the presence of petrobactin-independent iron acquisition pathways. One such pathway involves the ferric ion-binding protein FbpA, as a ΔfbpA mutant exhibits reduced growth on all substrates tested under iron limitation. Notably, the double mutant (ΔasbABF ΔfbpA) failed to grow, demonstrating that petrobactin and FbpA contribute to two distinct major iron acquisition pathways. The siderophore-dependent and -independent pathways appear to be largely functionally redundant and are involved in iron acquisition in all growth modes on all carbon sources tested.