An Fe(II)-containing medium was prepared by adding a 1 M FeCl2 stock solution to a
concentration of 10 mM and filtering the medium after storage for 48 h at 4°C to remove Fe(II)
precipitates, leading to a final concentration of ~8 mM of dissolved Fe(II) for low phosphate
mineral medium or ~ 4 mM for mineral medium. Photoferrotrophic strains were cultivated either
with Fe(II) as electron donor or in Fe(II)-free medium with 5 mM sodium acetate or H2
supplemented to the headspace as a H2/CO2 mixture (90:10 v/v) under constant light conditions
(True Light 15W/5500K) at 20°C.