| Comments |
P.484 right column bottom paragraph: "Fe has a special position in group V. It exists as Fe(III) under oxic conditions, which precipitates as insoluble hydroxide [ref 34]. This would mean that iron should have low bio-availability and not be widely used as a bio-element. The contrary is, however, the case. Fe is the transition metal with the highest number of atoms in the C. metallidurans cell (Table 1)[primary source 45]. This has “historical” reasons: before molecular oxygen became available on earth, that is before the first great oxygenation event 2.4 billion years ago [ref 46], Fe existed as Fe(II) that was largely bio-available and used in early life forms [ref 47]. After this event, cells were confronted with a massive iron starvation condition due to Fe(III) hydroxide precipitation, which was solved by the evolution of siderophore-dependent Fe(III) import pathways [refs 48, 49]. In anoxic environments, Fe(II) is still the predominant and readily available form of iron. This is the reason for the observed discrepancy that Fe is indicated as of low availability in Fig. 2 but as an important bio-element in Table 1." See notes beneath table |