There is some evidence that the virulence of some pathogenic bacteria is related to their iron uptake system. To better understand this system, three genes involved in iron uptake of Photobacterium damselae subsp. piscicida (tonB1, tonB2 and iron uptake regulator or fur) were cloned from a genomic library and sequenced. The amino acid sequence identities of tonB1 and tonB2 with the corresponding sequences of Vibrio spp. range from 32.4 to 39.5% and from 43.6 to 50.5%, respectively. The amino acid sequence identities of fur with the corresponding sequences of other Vibrio spp. are over 85%. We were able to construct a fur gene knock-out mutant using the marker exchange method. Using this knock-out mutant, we showed that tonB1, but not tonB2, is regulated by fur in P. damselae subsp. piscicida . The fur gene is also important for iron regulation since it has an influence on the expression of the heme receptor gene, hutA . The fur gene knock-out mutant generated in this study will be helpful in future studies of determining the role of iron in P. damselae subsp. piscicida pathogenesis and virulence.
