Photoferrotroph R. palustris TIE-1

The underlying adaptations required by anoxygenic phototrophs to oxidize Fe(II), a potential stressor, are not well constrained. We used quantitative proteomics to compare cells of the photoferrotroph Rhodopseudomonas palustris TIE-1 grown photoautotrophically with Fe(II) or H2, and photoheterotrophically with acetate. We observed unique proteome profiles for each condition with differences primarily driven by carbon source. Growth on Fe(II) was characterized by a response typical of iron homeostasis which included an increased abundance of proteins required for metal efflux (particularly copper), and decreased abundance of iron import proteins, including siderophore receptors, with no evidence of further stressors such as oxidative damage. This study suggests that the main challenge facing photoferrotrophs comes from limitations imposed by autotrophic growth and, once this challenge is overcome, iron stress can be mitigated using iron management mechanisms common to diverse bacteria.