Two types of 16S rRNA gene are found in Campylobacter helveticus: analysis, applications and characterization of the intervening sequence found in some strains

摘要

In the recently described species Campylobacter helveticus, two sizes of PCR amplicon were detected with primers homologous to conserved regions of the 16S rRNA gene. A conventionally sized gene was sequenced from the type strain, NCTC 12470, placing the new species as phylogenetically related to C. upsaliensis and the thermotolerant campylobacters. This nucleotide sequence enabled PCR primers to be designed for use in rapid molecular identification of C. helveticus and its closest phylogenetic relative, C. upsaliensis. When this assay was employed to characterize 22 ‘C. upsaliensis-like’ isolates, twelve were identified as C. helveticus and nine as C. upsaliensis, in agreement with data obtained with a C. helveticus-specific DNA probe. A 550 bp amplicon internal to the 16S rRNA gene of C. helveticus was used to determine restriction fragment length polymorphisms (RFLPs) in genomic Southern blots, confirming that the copy number of the C. helveticus gene was three, and identifying nine 16S rRNA gene profiles. In 5/12 C. helveticus isolates identified by PCR, an enlarged amplicon was detected. The enlarged 16S rRNA gene of one of these strains, NCTC 12838, was sequenced and shown to contain an atypical intervening sequence (IVS) of 148 nucleotides. The position and size of such an IVS was inferred in the other four isolates by PCR with primers 5′ and 3′ to its position in NCTC 12838. This is a first report of an IVS in the 16S rRNA gene of a eubacterium.