Amphi-enterobactin commonly produced among Vibrio campbellii and Vibrio harveyi strains can be taken up by a novel outer membrane protein FapA that also can transport canonical Fe(III)-enterobactin.

Abstract

Vibrio campbellii BAA-1116 (formerly Vibrio harveyi) is a model organism for quorum sensing study and produces the siderophores anguibactin and amphi-enterobactin. This study examined the mechanisms and specificity of siderophore uptake in V. campbellii and V. harveyi, and surveyed the diversity of siderophore production in V. campbellii and V. harveyi strains. The amphi-enterobactin gene cluster of BAA-1116 harbors a gene, named fapA, that is a homologue of genes encoding Fe(III)-siderophore-specific outer membrane receptors. Another strain, V. campbellii HY01, a strain pathogenic to shrimp, also carries this cluster including fapA. Our siderophore bioassay results using HY01-derived indicator strains show that the FapA protein localized in the outer membrane fraction of V. campbellii HY01 is essential for the uptake of Fe(III)-amphi-enterobactin as well as exogenous siderophores, including enterobactin from E. coli, but not vanchrobactin from V. anguillarum RV22 while Fe(III)-amphi-enterobactin can be utilized by V. anguillarum. Electrospray ionization mass spectrometry as well as bioassay revealed that various V. campbellii and V. harveyi strains produce a suite of amphi-enterobactins with various fatty acid appendages, including several novel amphi-enterobactins, and these amphi-enterobactins can be taken up by V. campbellii HY01 via FapA, indicating that amphi-enterobactin production is a common phenotype among V. campbellii and V. harveyi, whereas our previous work, confirmed herein, showed that anguibactin is only produced by V. campbellii strains. These results along with the additional finding that a 2,3-dihydroxybenzoic acid biosynthesis gene, aebA, located in the amphi-enterobactin gene cluster, is essential for both anguibactin and amphi-enterobactin biosynthesis, suggest the possibility that amphi-enterobactin is a native siderophore of V. campbellii and V. harveyi, while the anguibactin system has been acquired by V. campbellii during evolution.