Bacillus subtilis bacteria hinder the oxidation and hydrolysis of Fe2+ ions

Bacteria are known to associate closely with secondary iron oxides in natural environments, but it is still unclear whether they catalyze their precipitation. Here, Fe2+ ions were progressively added to various concentrations of Bacillus subtilis bacteria in permanently oxic conditions while maintaining the pH at 6.5 by adding a NaOH solution at a monitored rate. The iron/ bacteria precipitates were characterized by wet chemistry, SEM, and XRD. Abiotic syntheses produced nanolepidocrocite, and their kinetics displayed a strong autocatalytic effect. Biotic syntheses led to the formation of tiny and poorly crystallized particles at intermediate bacterial concentrations and to a complete inhibition of particle formation at high bacterial concentrations. The occurrence of the autocatalytic effect was delayed and its intensity was reduced. Both the oxidation and the hydrolysis of Fe2+ ions were hindered.