The yctCBA operon of Yersinia ruckeri, involved in in vivo citrate uptake, is not required for virulence

Abstract

A three-gene operon, named yctCBA (Yersinia citrate transporter), induced by citrate and repressed by glucose was identified from a previously selected in vivo-induced (ivi) clone in the fish pathogen Yersinia ruckeri. Interestingly, despite being an ivi clone, the drastic growth reduction of the yctC mutant in the presence of citrate, and the relatively high content of this compound in rainbow trout serum, the operon was not required for virulence.

FIG. 1.

Chromosomal organization of the region containing the yctCBA operon in Y. ruckeri 150R. The direction of transcription is indicated by arrows. The arrangement of the transcriptional fusion between ytcC and the promoterless genes lacZY in the Y. ruckeri 150RiviIX strain is shown below the map. The putative promoter (P) selected by IVET is indicated, as well as the catseq2 oligonucleotide used to sequence the fragment adjacent to the pIVET8 integration site. The black circle represents the pIVET8 replication origin. S, SalI site; Sp, SphI site; yctC', initial 424 bp of the yctC gene; yctC⁺, complete copy of the yctC gene; cat, chloramphenicol acetyltransferase gene (promoterless); lacZY, genes for lactose fermentation (promoterless); bla, ampicillin resistance gene.

FIG. 2.

Growth curves of Y. ruckeri 150R and yctC mutant strains in different media. Aliquots of overnight cultures were used to inoculate 250-ml flasks containing 20-ml portions of the different media, and cultures of Y. ruckeri 150R (▪) and yctC mutant (⋄) were grown at 18°C and 250 rpm in the different media. The media used were M9C medium plus 0.5% glucose (solid black line),M9C medium plus 25 mM trisodium citrate (broken line), and M9C medium (dotted line). Growth was monitored by determining the optical density at 600 nm (OD₆₀₀) of the culture. The values are the averages for three independent experiments.