To identify genes that enable the enteric redmouth disease bacterium, Yersinia ruckeri, to persist in salmonid fish, 1056 signature-tagged mini-Tn5Km2 transposon mutants of a serotype 1 strain of Y. ruckeri,
RS1154, were screened in rainbow trout by immersion
infection. Two rounds of screening in fish identified 25 mutants that were not re-isolated from the kidney, 7 days post-
infection. Six mutants were tested a third time in fish, in 1:1 competitive challenges with the parent strain; 4 failed to establish in kidney and 2 were present at low levels compared to the parent. Sequence analyses from the single transposon insertion sites in each of the 25 mutants identified genes with sequence homologies to genes for ZnuA, a periplasmic
zinc-binding protein of ZnuABC transporter; the UvrY response regulator of BarA-UvrY two-component system; a PtrA
protease of the
insulin-degrading enzyme family; the RcpA
protein of type IV bundle-forming pili; the ParA
ATPase of a ParAB
DNA-partitioning system; a Wzy polymerase; a
polysaccharide deacetylase; a transporter belonging to the major facilitator superfamily and 7 hypothetical
proteins of unknown function. The products of 5 of these mutated genes have predicted functions associated with cell surfaces or membranes, which could be important for survival of Y. ruckeri in rainbow trout, while other putative gene products could contribute to
infection and invasion processes.