Interstrain Gene Transfer inChlamydia trachomatisIn Vitro: Mechanism and Significance

Abstract

The high frequency of between-strain genetic recombinants of Chlamydia trachomatis among isolates obtained from human sexually transmitted infections suggests that lateral gene transfer (LGT) is an important means by which C. trachomatis generates variants that have enhanced relative fitness. A mechanism for LGT in C. trachomatis has not been described, and investigation of this phenomenon by experimentation has been hampered by the obligate intracellular development of this pathogen. We describe here experiments that readily detected LGT between strains of C. trachomatis in vitro. Host cells were simultaneously infected with an ofloxacin-resistant (Ofx r ) mutant of a serovar L1 strain (L1:Ofx r -1) and a rifampin-resistant (Rif r ) mutant of a serovar D strain (D:Rif r -1). Development occurred in the absence of antibiotics, and the progeny were subjected to selection for Ofx r Rif r recombinants. The parental strains differed at many polymorphic nucleotide sites, and DNA sequencing was used to map genetic crossovers and to determine the parental sources of DNA segments in 14 recombinants. Depending on the assumed DNA donor, the estimated minimal length of the transferred DNA was >123 kb in one recombinant but was >336 to >790 kb in all other recombinants. Such trans-DNA lengths have been associated only with conjugation in known microbial LGT systems, but natural DNA transformation remains a conceivable mechanism.LGT studies can now be performed with diverse combinations of C. trachomatis strains, and they could have evolutionary interest and yield useful recombinants for functional analysis of allelic differences between strains.

Transformation and isolation of allelic exchange mutants of Chlamydia psittaci using recombinant DNA introduced by electroporation

“…Although interstrain, intergenic, and intragenic recombination has been proposed to generate sequence variations in chlamydiae (15,16), this study proves that recombinant DNA can be introduced into C. psittaci 6BC and promote recombination/exchange of ''heterologous'' DNA sequences into the bacterial chromosome.…”

Generation of targeted Chlamydia trachomatis null mutants

“…Because the goal of our study was to generate isogenic C. trachomatis mutants, the desired mutation frequency was one mutation per genome. The C. trachomatis genome contains ∼4.3 × 10 5 C-G base pairs, and transitions of five of these C-G pairs can yield Rif R (6,(13)(14)(15)(16)(17). Thus, we estimated that a Rif R frequency of 1.16 × 10 −5 [1/(4.3 × 10 5 /5) = 1.16 × 10 −5 ] corresponded to a predicted level of mutagenesis that would result in a single C-G base pair mutation per genome (Table S1).…”

Chlamydial Intracellular Survival Strategies

“…In landmark experiments, Robert DeMars provided evidence of DNA exchange among Chlamydiae in the laboratory (Demars et al 2007;DeMars and Weinfurter 2008). In cells coinfected with C. trachomatis serovars that were naturally resistant to ofloxacin or to rifampin, doubly drug-resistant recombinant Chlamydia arose at 10 4 times higher frequency than that of spontaneous mutations, and the genomes of these recombinants were chimeric recombinants of the parental strains.…”