Mapping and Regulation of Genes within Salmonella Pathogenicity Island 12 That Contribute to
In Vivo
Fitness of Salmonella enterica Serovar Typhimurium
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abstract
ABSTRACTSalmonella
pathogenicity island 12 (SPI-12) of
Salmonella enterica
serovar Typhimurium is a 15-kb region that encompasses genes
STM2230
to
STM2245
and encodes a remnant phage known to contribute to bacterial virulence. In mouse infection experiments and replication assays in macrophages, we demonstrated a role for four genes in SPI-12 for bacterial survival in the host. STM2239, a potential Q antiterminator, showed a prominent contribution to bacterial fitness. Transcriptional reporter experiments, quantitative reverse transcription-PCR (RT-PCR), and immunoblotting demonstrated that the virulence regulator SsrB and STM2239 contribute to transcriptional activation of genes in SPI-12. SsrB was found to indirectly regulate this locus by transcriptional read-through from the
sspH2
(
STM2241
) promoter. Chromatin immunoprecipitation showed that STM2239 copurified with the promoter regulating
STM2237
, suggesting that STM2239 may function as an antiterminator to activate adjacent genes. These results demonstrate that bacteriophage genes may be adapted by pathogenic bacteria to improve fitness in the host.
