{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T16:07:15Z","timestamp":1753891635054,"version":"3.41.2"},"reference-count":30,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2023,2,1]],"date-time":"2023-02-01T00:00:00Z","timestamp":1675209600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Microbiol."],"abstract":"<jats:p><jats:italic>Vibrio cholerae<\/jats:italic> serogroup O1 (<jats:italic>V. cholerae<\/jats:italic> O1) is closely associated with cholera epidemics and has two main immunologically distinguishable serotypes, Ogawa and Inaba. Isolates serotype as Ogawa if the O-antigen polysaccharide (O-PS) is methylated or as Inaba if the O-PS is not methylated. This methylation is mediated by a methyltransferase encoded by the <jats:italic>rfbT<\/jats:italic> gene, and the mutation and low expression of <jats:italic>rfbT<\/jats:italic> results in serotype switch from Ogawa to Inaba. Previously, we have shown that cAMP receptor protein (CRP) activates <jats:italic>rfbT<\/jats:italic>. In this study, we demonstrated that histone-like nucleoid structuring protein (H-NS) is directly involved in the transcriptional repression of <jats:italic>rfbT<\/jats:italic>. This finding is supported by the analyses of <jats:italic>rfbT<\/jats:italic> mRNA level, <jats:italic>rfbT<\/jats:italic>-<jats:italic>lux<\/jats:italic> reporter fusions, electrophoretic mobility shift assay (EMSA), and DNase I footprinting assay. The <jats:italic>rfbT<\/jats:italic> mRNA abundances were significantly increased by deleting <jats:italic>hns<\/jats:italic> rather than <jats:italic>fis<\/jats:italic> which also preferentially associates with AT-rich sequences. A <jats:italic>single-copy chromosomal complement of hns partly restored the down-regulation of rfbT<\/jats:italic>. Analysis of <jats:italic>rfbT<\/jats:italic>-<jats:italic>lux<\/jats:italic> reporter fusions validated the transcriptional repression of <jats:italic>hns.<\/jats:italic> Subsequent EMSA and DNase I footprinting assay confirmed the direct binding of H-NS to <jats:italic>rfbT<\/jats:italic> promoter and mapped the exact binding site which was further verified by site-directed mutagenesis and promoter functional analysis. Furthermore, we found that in <jats:italic>hns<\/jats:italic> deletion mutant, CRP is no longer required for transcriptionally activating <jats:italic>rfbT<\/jats:italic>, suggesting that CRP functions as a dedicated transcription factor to relieve H-NS repression at <jats:italic>rfbT<\/jats:italic>. Together, this study expanded our understanding of the genetic regulatory mechanism of serotype conversion by global regulators in <jats:italic>V. cholerae<\/jats:italic> O1.<\/jats:p>","DOI":"10.3389\/fmicb.2023.1111895","type":"journal-article","created":{"date-parts":[[2023,2,1]],"date-time":"2023-02-01T08:58:40Z","timestamp":1675241920000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Serotype conversion gene rfbT is directly regulated by histone-like nucleoid structuring protein (H-NS) in V. cholerae O1"],"prefix":"10.3389","volume":"14","author":[{"given":"Yu","family":"Han","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jing","family":"Li","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"He","family":"Gao","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xiaorui","family":"Li","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ran","family":"Duan","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Qian","family":"Cheng","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Biao","family":"Kan","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Weili","family":"Liang","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1965","published-online":{"date-parts":[[2023,2,1]]},"reference":[{"key":"ref1","doi-asserted-by":"publisher","first-page":"e0005045","DOI":"10.1371\/journal.pntd.0005045","article-title":"Major shift of toxigenic V. cholerae O1 from Ogawa to Inaba serotype isolated from clinical and environmental samples in Haiti","volume":"10","author":"Alam","year":"2016","journal-title":"PLoS Negl. 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