Distribution of plasmid- and chromosome-mediated iron uptake systems in Vibrio anguillarum strains of different origins

Abstract

We investigated the incidence of plasmid-mediated and chromosome-mediated iron uptake systems in strains of Vibrio anguillarum that belong to serotypes 01 and 02 and were isolated from different fish species and in different geographic areas. All of the strains gave positive reactions in CAS agar medium and in the Arnow test, which indicated that catechol types of siderophores were produced. The majority of V. anguillarum serotype 01 strains harbored a 65-kb plasmid similar to plasmid pJMl from strain 775, which encodes the siderophore anguibactin and its outer membrane receptor, protein OM2. All of the isolates harboring this plasmid promoted the growth of an anguibactin-deficient receptor-proficient mutant derived from strain 775, but none of these isolates promoted the growth of mutants lacking receptor OM2. Furthermore, under iron-limiting conditions all of these strains induced outer membrane proteins that were identical in size to protein OM2 of strain 775. In contrast, none of the serotype 02 strains contained a high-molecular-weight plasmid, but all of them induced the growth of mutants defective in the anguibactin-mediated system regardless of the presence or absence of receptor OM2. The serotype 02 strains, but not the plasmid-bearing serotype 01 strains, also induced the growth of Salmonella typhimurium enb-1 which utilizes only enterobactin as a siderophore. Moreover, the pattern of iron-regulated outer membrane proteins in serotype 02 isolates was totally different from the pattern in the serotype 01 strains harboring the 65-kb plasmid. Interestingly, several plasmidless strains belonging to serotype 01 behaved in the same way as serotype 02 strains in cross-feeding experiments and produced the same iron-regulated outer membrane protein patterns. These results indicate that regardless of their origins all V. anguillarum strains belonging to serotype 02 contain similar chromosome-mediated iron-sequestering systems. However, in the serotype 01 strains both chromosome-and plasmid-encoded iron uptake systems occur, but there is a significant predominance of the plasmid-mediated system.

A comprehensive review of Vibrio (Listonella) anguillarum: ecology, pathology and prevention

“…A second iron-uptake system is present in V. anguillarum which functions independently of the pJM1 ironsequestering system and its respective OM2 receptor protein, based on chromosomally encoded mediation (Lemos et al 1988). The pJM1 plasmid series is present in most V. anguillarum O1 strains but is absent in serotype O2 while the chromosome-mediated iron-uptake system exists in both the O1 and O2 serotype (Conchas et al 1991). Vibrio anguillarum biotypes which exhibit chromosomemediated iron uptake do so using the siderophore vanchrobactin as opposed to anguibactin which is used in plasmidmediated iron uptake (Mackie & Birkbeck 1992;Soengas et al 2006).…”

Anguibactin‐ versus vanchrobactin‐mediated iron uptake in Vibrio anguillarum: evolution and ecology of a fish pathogen

“…, 2009). It is unclear which is the possible role, if any, of these genes in the chromosome, although it seems clear that they are not expressed, at least in serotype O2 strains, since they are disrupted by IS elements and FatA protein was never detected in serotype O2 strains (Conchas et al. , 1991; Balado et al.…”

“…Interestingly, there are some highly virulent serotype O1 strains that do not harbour pJM1‐like plasmids. Iron uptake in these strains is actually mediated by vanchrobactin (Conchas et al. , 1991; Naka et al.…”

“…On the other hand, all serotype O2 strains tested so far, and some plasmidless serotype O1 strains, produce a catecholate‐type siderophore that is not related to the pJM1‐mediated system (Lemos et al. , 1988; Conchas et al. , 1991).…”

Two ABC transporter systems participate in siderophore transport in the marine pathogenVibrio anguillarum775 (pJM1)

“…In addition to anguibactin, V. anguillarum 775 (pJM1) can transport exogenous siderophores such as vanchrobactin and enterobactin (Naka et al, 2008;Balado et al, 2009;. One of them, vanchrobactin, is a chromosomally encoded siderophore produced by natural pJM1-less V. anguillarum O1 strains and other serotype strains (Lemos et al, 1988;Conchas et al, 1991;Balado et al, 2006Balado et al, , 2008Soengas et al, 2006). We previously showed that outer membrane proteins, FvtA and FetA, are involved in the transport of these exogenous siderophores in V. anguillarum 775(pJM1) .…”