RESUMO
The effects of iron limitation on growth, the composition and function of the respiratory chains, and gallium uptake in Escherichia coli have been studied. Decreasing the iron concentration in a defined medium using Chelex resin gave lower growth yields in both continuous culture and prolonged batch culture. In the former, iron-limited (entering [Fe] less than or equal to 2.0 microM) cells exhibited diminished respiration rates, respiration-driven proton translocation quotients, and levels of non-haem iron and cytochromes. The cellular concentration of haemoprotein b-590 (a cytochrome alpha 1-like hydroperoxidase) decreased 20-fold on iron limitation, whilst a CO-binding pigment with an absorption maximum in the dithionite-treated form near 500 nm appeared. Gallium(III) (9 microM) added to iron-limited, but not iron-sufficient, cultures diminished growth yields further; cells grown with low entering concentrations of iron took up less gallium than iron-sufficient cells. These results are attributed to the interference by gallium(III) with siderophore-mediated metal uptake. Gallium also stimulated iron uptake and was itself accumulated by iron-sufficient cells, suggesting that gallium(III) also affects the iron transport system(s) of low affinity.