Because of its physicochemical properties iron is an indispensable micronutrient for virtually all bacterial species. On the other hand, excess of iron could promote via the Fenton reaction formation of reactive oxygen species (ROS), which could be toxic for the cell. Therefore, microorganisms have established a tight control on the intracellular iron content so that it meets the metabolic needs of the cell. The milestone of the bacterial iron-dependent response is the so-called ferric uptake regulator (Fur) protein.
Comparative in silico, biochemical and in vivo studies established the role of CAC1682 as a genuine iron-responsive regulator (CacFur) in the solvent-producing bacterium Clostridium acetobutylicum. In order to determine the role of Fur in C. acetobutylicum, the fur gene was disrupted by insertional mutagenesis using the Clostron® system. The resultant fur defective strain exhibited a slow-growing phenotype, increased intracellular iron content and enhanced sensitivity to oxidative stress. Furthermore, to get insights into the mechanisms for maintenance of iron homeostasis in C. acetobutylicum, the transcriptional modifications in response to iron limitation and inactivation of fur were determined and compared. Bioinformatic analysis of the promotor sequences of the genes, which elicited changes in transcription under both conditions allowed the indentification of the putative direct targets of CacFur (CacFur regulon).