Iron quantification was carried out in microtiter plates with a modified spectrophotometric
ferrozine assay (Stookey, 1970), as described previously (Muehe et al., 2009). Samples from
photoferrotrophic cultures were acidified with 1 M HCl to stabilize Fe(II). Ferrozine
measurements were performed in triplicate and measured with a spectrophotometric plate reader
(