Mercury (Hg) is the most highly toxic heavy metal, and must be removed from waterways to very low levels. Biologically mediated mercury removal is an emerging technology that has the potential to be robust, efficient and cost-effective. In this study, the impact of carbon source on the behaviour and microbial community composition of mixed microbial cultures was evaluated, and their performance was compared with a pure culture of Pseudomonas putida spi3. Glucose and acetate. two carbon sources that are commonly present in wastewaters, were chosen for this study. Distinct microbial populations were enriched with each carbon source. Glucose led to a more suitable microbial culture for Hg2+ bioreduction that was able to reduce Hg2+ at faster rates when compared to acetate. Furthermore, acetate consistently led to poorer process performance, irrespective of the microbial culture, possibly due to the formation of mercuric acetate complexes. It is proposed that glucose can be a more beneficial carbon source than acetate for the successful operation of Hg bioremediation systems. (C) 2008 Elsevier B.V. All rights reserved.