Abstract
Unlike the majority of Salmonella enterica serovars, Salmonella Typhi (S. Typhi), the etiological agent of human typhoid, is monophasic. S. Typhi normally harbours only the phase 1 flagellin gene (fliC), which encodes the H:d antigen. However, some S. Typhi strains found in Indonesia express an additional flagellin antigen termed H:z66. Molecular analysis of H:z66+ S. Typhi revealed that the H:z66 flagellin structural gene (fljBz66) is encoded on a linear plasmid that we have named pBSSB1. The DNA sequence of pBSSB1 was determined to be just over 27 kbp, and was predicted to encode 33 coding sequences. To our knowledge, pBSSB1 is the first non-bacteriophage–related linear plasmid to be described in the Enterobacteriaceae.
Highlights
Flagella play a critical role in the lifestyle of many bacteria, and the flagellin subunit is an important target for pathogen recognition by the mammalian innate immune system through Toll-like receptor (TLR) 5 [1]
Salmonella enterica serovar Typhi (Typhi) strains isolated in Indonesia express an alternative H antigen, known as H:j, and/or a second flagellin, called H:z66 [5]
Linear DNA replicons are extremely rare in enteric bacteria, and those that have been described, including PY54 of Yersinia enterocolitica [26], N15 of E. coli [25], and PKO2 of Klebsiella oxytoca [27], are linear hairpin-ended prophage
Summary
Flagella play a critical role in the lifestyle of many bacteria, and the flagellin subunit is an important target for pathogen recognition by the mammalian innate immune system through Toll-like receptor (TLR) 5 [1]. Antiserum against flagella (H antigen) and lipopolysaccharide (O antigen) are the cornerstone of Salmonella classification through the Kauffmann–White scheme [2], which divides Salmonella enterica into the various serovars. The majority of S. enterica serovars are biphasic, alternating expression between two flagellar antigens through a process called ‘‘phase variation’’ [3]. One of the two flagellin genes, fliC and fljB, which are located at distinct loci on the Salmonella chromosome, is expressed at any given time [4]. Typhi), the cause of the human systemic infection known as typhoid, is normally monophasic, harbouring only the phase 1 flagellin gene fliC, which encodes the H:d antigen, and lacking a fljB equivalent. Typhi strains isolated in Indonesia express an alternative H antigen, known as H:j, and/or a second flagellin, called H:z66 [5]. Whilst H:j variants arise through a deletion within the fliC gene [6], the H:z66 antigen is encoded on an unlinked locus
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