Iron is essential for growth in both bacteria and mammals. Controlling the amount of free iron in solution is often used as a tactic by hosts to limit invasion of pathogenic microbes; binding iron tightly within protein molecules can accomplish this. Such iron-protein complexes include haem in blood, lactoferrin in tears/saliva and transferrin in blood plasma. Some bacteria express surface receptors to capture eukaryotic iron-binding compounds, while others have evolved siderophores to scavenge iron from iron-binding host proteins [<cite idref="PUB00006650"/>].<p> The absence of free iron molecules in the surrounding environment triggers transcription of gene clusters that encode both siderophore-synthesis enzymes, and receptors that recognise iron-bound siderophores [<cite idref="PUB00006626"/>]. Classic examples are the enterobactin/enterochelin clusters found in <taxon tax_id="562">Escherichia coli</taxon> and Salmonella, although similar moieties in other pathogens have been identified. The enzymic machinery that produces vibrionectin in <taxon tax_id="666">Vibrio cholerae</taxon> is such a homologue [<cite idref="PUB00006668"/>].</p><p>EntA, a 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase enzyme, is involved in the third stage of enterobactin biosynthesis and converts isochorismate to 2,3-dihydroxybenzoic acid (DHBA). Deletion studies involving EntA- mutants have shown that it is essential for virulence [<cite idref="PUB00006627"/>]. </p> 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase