Iron availability in mixed cultures of sulfate‐reducing bacteria

Abstract

Postgate's medium C was found to be unsuitable for quantitative studies of mixed microbial cultures containing sulfate-reducing bacteria. Equilibrium calculations of iron concentration, along with the experimental observations show that precipitation of iron occurs in Postgate's medium, despite the presence of citrate and yeast extract. The often ascribed inhibitory effect of sulfide on the growth of sulfate-reducing bacteria may be largely due to the reduced availability of iron, as a result of the precipitation of ferrous sulfide. Because it is essential to clearly define the growth limiting nutrient when carrying out quantitative bacterial growth studies, yeast extract should be excluded from the culture medium. Single-phase, exponential growth was observed for mixed cultures containing sulfate-reducing bacteria, using a chemically defined medium that incorporated the metal complexing agent EDTA. When carrying out quantitative kinetic studies of sulfate-reducing bacteria, a chemically defined medium incorporating EDTA is recommended.