DIVERSITY OF SIDEROPHORE GENES ENCODING BIOSYNTHESIS OF 2,3-DIHYDROXYBENZOIC ACID IN AEROMONAS SPP

Most species of the genus Aeromonas produce the siderophore amonabacti n, although two species produce enterobactin, the siderophore of many enteric bacteria. Both siderophores contain 2,3-dihydroxybenzoic acid (2,3-DHB). Siderophore genes (designated aebC, -E, -B and -A, for aero monad enterobactin biosynthesis) that complemented mutations in the en terobactin genes of the Escherichia coli 2,3-DHB operon, entCEBA(P15), were cloned from an enterobactin-producing isolate of the Aeromonas s pp. Mapping of the aeromonad genes suggested a gene order of aebCEBA, identical to that of the E. coli 2,3-DHB operon. Gene probes for the a eromonad aebCE genes and for amoA (the entC-equivalent gene previously cloned from an amonabactin-producing Aeromonas spp.) did not cross-hy bridize. Gene probes for the E. coli 2,3-DHB genes entCEBA did not hyb ridize with Aeromonas spp. DNA. Therefore, in the genus Aeromonas, 2,3 -DHB synthesis is encoded by two distinct gene groups; one (amo) is pr esent in the amonabactin-producers, while the other (aeb) occurs in th e enterobactin-producers. Each of these systems differs from (but is f unctionally related to) the E. coli 2,3-DHB operon. These genes may ha ve diverged from an ancestral group of 2,3-DHB genes.