Functional characterization of IScs605, an insertion element carried by tetracycline-resistant Chlamydia suis

Abstract

Stable tetracycline resistance in Chlamydia suis is mediated by a family of genomic islands [the tet(C) islands] that are integrated into the chlamydial chromosome. The tet(C) islands contain several plasmid-specific genes, the tet(C) resistance gene and, in most cases, a novel insertion element (IScs605) encoding two predicted transposases. The hypothesis that IScs605 mediated the integration of the tet(C) resistance islands into the C. suis genome was tested using a plasmid-based transposition system in Escherichia coli. Both high-and medium-copy-number plasmids were used as carriers of IScs605 in these experiments. IScs605 integrated into a target plasmid (pOX38) when delivered by either donor plasmid, and integration of the entire donor plasmid was common. IScs605-mediated integration occurred at many positions within pOX38, with 36 of 38 events adjacent to a 59-TTCAA-39 sequence. Deletions in each of the candidate transposase genes within IScs605 demonstrated that only one of the two ORFs was necessary for the observed transposition activity and target specificity. Analysis of progeny from the mating assays also indicated that IScs605 can excise following integration into a target DNA, and, in each tested case, the sequence 59-AATTCAA-39 remained at the site of excision. Collectively, these results are consistent with the nucleotide sequence data collected for the tet(C) islands, and strongly suggest that a transposase within IScs605 is responsible for integration of these genomic islands into the C. suis chromosome.

Amoebal Endosymbiont Neochlamydia Genome Sequence Illuminates the Bacterial Role in the Defense of the Host Amoebae against Legionella pneumophila

“…It has been reported that Chlamydia suis possesses a novel insertion element (IScs605) encoding two predicted transposases [46], and that Protochlamydia UWE25 contains 82 transposases [47]. Thus, the features of the Neochlamydia S13 genome were unique, without genome reduction, but with specified genes for controlling host-parasite interaction, resulting in successful adaptation to the host amoeba.…”

Expression and Targeting of Secreted Proteins from Chlamydia trachomatis

“…Many strains of C. suis, a pathogen of swine, contain a transposon-mediated tetracycline resistance cassette integrated into the chromosome (53,54). These resistance cassettes share a high degree of sequence similarity to resistance plasmids from a variety of bacterial species and may have been selected for in C. suis as a result of exposure to antibiotic containing feed (53,54). Subsequently, recombination between C. trachomatis stains in coinfected cultures was demonstrated (55)(56)(57)(58).…”

“…Chlamydiae have been known for some time now to have the capacity for genetic recombination. Many strains of C. suis, a pathogen of swine, contain a transposon-mediated tetracycline resistance cassette integrated into the chromosome (53,54). These resistance cassettes share a high degree of sequence similarity to resistance plasmids from a variety of bacterial species and may have been selected for in C. suis as a result of exposure to antibiotic containing feed (53,54).…”

Horizontal Transfer of Tetracycline Resistance among Chlamydia spp. In Vitro

“…Pigs are routinely fed tetracycline during growth in production facilities, and therefore the ability to grow in low levels of this drug remains a major selective force for porcine commensals and pathogens. The entry of the resistance gene into the population may have led to rapid clonal proliferation within an unexploited niche, followed by homologous recombination between different C. suis strains, and likely at least some activity by the transposase encoded by IScs605, to generate the family of tet(C) islands currently found in C. suis (9). The overriding hypothesis in this scenario is that the entry of the genomic island into C. suis was initially challenging in this natural system, but transfer among strains, via a homologous-recombination process similar to that demonstrated in this report, was straightforward and perhaps rapid.…”