RNA analysis indicated that mhuA and mhuB are each transcribed from individual Fur-regulated promoters. GSK-3 activity Moreover, RNA analysis of an mhuB deletion mutant and a promoter reporter assay coupled with β-galactosidase suggested that MhuB could function as an activator for mhuA transcription. Finally, the role of MhuA as the heme/hemoglobin receptor was confirmed by construction of an mhuA deletion mutant and its complemented strain followed by growth assay. Iron is an element integral to the growth of almost all bacteria.

However, the availability of iron for bacteria is limited because it is usually present as insoluble ferric hydroxide polymers in an aerobic environment or bound to iron-binding proteins such as transferrin and lactoferrin in mammalian hosts (1). Therefore, most bacteria have

evolved the ability to acquire iron under iron-restricted conditions. Numerous bacteria produce and secrete siderophores (low-molecular weight iron-binding chelators) which can remove ferric iron from iron-binding proteins. In Gram-negative bacteria, ferric ion complexed with siderophore (ferrisiderophore) is transported into cells via a TonB-dependent specific uptake system, consisting of an outer membrane receptor protein and an ABC transporter (2). In addition, certain bacteria acquire heme as a nutritional iron source by a TonB-dependent system, similar Maraviroc solubility dmso to those for ferrisiderophores, which includes the binding of heme or heme-containing proteins such as hemoglobin to the cell surface receptor, followed by transport of the intact heme moiety into the cell (3). Siderophores are unable to remove the iron from heme. Moreover, when intracellular iron concentrations are high, expression of those systems studied to next date is negatively regulated at the transcriptional level by a global iron-binding repressor protein called Fur (ferric uptake regulation) with ferrous ion as a corepressor, (4, 5). V. mimicus was first described as a group of biochemically atypical strains of V. cholerae

(6) but they share some pathogenic factors such as enterotoxins and hemolysins (7). V. mimicus, like other pathogenic Vibrio species, inhabits environmental water, including river, brackish, and sea water, and causes diarrhea through eating fish and shellfish contaminated with the bacterium (8). The present authors have previously reported that V. mimicus secretes the siderophore aerobactin in response to iron restriction (9), and that the iucABCD genes engage in aerobactin biosynthesis. They have also reported that the ferriaerobactin complex is incorporated into the cytosol via the 77-kDa IROMP, IutA, and the ABC transporter, MatCDB (10). V. mimicus also expresses 80-kDa IROMP under iron-restricted conditions (9). Hence, V. mimicus is expected to use at least one other iron source besides ferriaerobactin. Although many Vibrio species, including V.