The Influence of Carbon Source on the Products of Dissimilatory Iron Reduction

We have examined the influence of carbon source on both the rate of iron reduction and the mineralogy of the reduction products with Shewanella putrefaciens strain W3-18-1. When pyruvate was the carbon source, the secondary products were spherules composed of siderite. When uridine was used as the carbon source, the products were hexagonal plate-like structures identified as iron carbonate hydroxide hydrate, also known as carbonate green rust, a precursor to fougerite. When lactate was used as the carbon source, products were a mixture of iron carbonate hydroxide and magnetite. In terms of reaction stoichiometry, there were differences in the amount of acetate produced depending on the starting organic carbon source. Incubation with pyruvate produced a relatively large amount of acetate compared to incubation with uridine and lactate. There were also differences in the final pH of the cultures. While the pH for incubations with lactate started at 8.6 and ended between 8.0-8.3, the pH of cultures incubated with uridine was found to be almost a full unit lower at the conclusion of the experiment (∼7.4). Solubility diagrams based on the chemistry found in our experiments predict that the production of Fe2+(aq) should always lead to the formation of magnetite. However, strain W3-18-1 produced different minerals depending on the carbon source utilized as the electron acceptor.