Bioreduction of iron compounds by Aeromonas hydrophila

• Aeromonas hydrophila showed a high Fe-reducing activity on the synthetic ferric solid.
• A. hydrophila showed a low Fe-reducing activity on the natural mineral.
• The bacterial growth rate were totally different for both solid substrates.
• The bioavailability of both iron sources was totally different.

The iron-reducing ability of a bacterial culture of Aeromonas hydrophila has been tested on two different ferric solid substrates: a natural mineral (containing goethite, FeO(OH), and hematite, Fe2O3), and a synthetic sodium jarosite (NaFe3(SO4)2(OH)6). Two fluid dynamic variables were investigated in the iron bioreduction process: pulp density and stirring speed. The maximum level of iron reduction was obtained with jarosite (87.8%) compared to 4% for the natural mineral. Similarly, cell numbers and bacterial growth kinetics were clearly different for both solid substrates. Unlike the natural ore, the number of microorganisms increased with increasing pulp density for jarosite. The effect of stirring on the iron bioreduction was more marked using the natural mineral than jarosite. The bioavailability of both iron sources was totally different. The results obtained suggest a different mechanism of bacterial attack: possibly direct for the synthetic jarosite and indirect for the natural mineral.