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Deletion of a previously uncharacterized flagellar-hook-length control gene fliK modulates the ⁵⁴-dependent regulon in Campylobacter jejuni

Nahid Kamal^1,

Aparna Jagannathan^1,

Gemma Marsden^4,

Jason Hinds^4,

¹ School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
² Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
³ Sainsbury Laboratory, John Innes Centre, Norwich NR4 7UH, UK
⁴ Department of Medical Microbiology, St George's Hospital Medical School, Cranmer Terrace, Tooting, London SW17 0RE, UK

Correspondence
Charles W. Penn
c.w.penn{at}bham.ac.uk

A previously unannotated, putative fliK gene was identified in the Campylobacter jejuni genome based on sequence analysis; deletion mutants in this gene had a ‘polyhook’ phenotype characteristic of fliK mutants in other genera. The mutants greatly overexpressed the ⁵⁴-dependent flagellar hook protein FlgE, to form unusual filamentous structures resembling straight flagella in addition to polyhooks. The genome sequence reveals only one gene predicted to encode an orthologue of the NtrC-family activator required for ⁵⁴-dependent transcription. Hence, all ⁵⁴-dependent genes in the genome would be overexpressed in the fliK mutant together with flgE. Microarray analysis of genome-wide transcription in the mutant showed increased transcription of a subset of genes, often downstream of ⁵⁴-dependent promoters identified by a quality-predictive algorithm applied to the whole genome. Assessment of genome-wide transcription in deletion mutants in rpoN, encoding ⁵⁴, and in the ⁵⁴-activator gene flgR, showed reciprocally reduced transcription of genes that were overexpressed in the fliK mutant. The fliA (²⁸)-dependent regulon was also analysed. Together the data clearly define the roles of the alternative sigma factors RpoN and FliA in flagellar biogenesis in C. jejuni, and identify additional putative members of their respective regulons.

Present address: Department of Haematological Medicine, King's College London, Rayne Institute, 123 Coldharbour Lane, London SE5 9NU, UK.

Present address: BBSRC Institute for Animal Diseases, Compton, Newbury RG20 7NN, UK.

Present address: Department of Genetics, University of Leicester, Leicester LE1 7RH, UK.

Supplementary tables listing the mutant genes up- or down-regulated by more than twofold compared with the wild-type and potential ⁵⁴-dependent promoters in C. jejuni are available with the online version of this paper.

The array design is available in µG@Sbase (accession no. A-BUGS-8; http://bugs.sgul.ac.uk/A-BUGS-8) and also ArrayExpress (accession no. A-BUGS-8).