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Effect of long-term laboratory propagation on Chlamydia trachomatis genome dynamics

2013; Elsevier BV; Volume: 17; Linguagem: Inglês

10.1016/j.meegid.2013.03.035

1567-7257

Vítor Borges, Rita Ferreira, Alexandra Nunes, Mafalda Sousa‐Uva, Miguel Abreu, Maria José Borrego, João Paulo Gomes,

Gut microbiota and health

It is assumed that bacterial strains maintained in the laboratory for long time shape their genome in a different fashion from the nature-circulating strains. Here, we analyzed the impact of long-term in vitro propagation on the genome of the obligate intracellular pathogen Chlamydia trachomatis. We fully-sequenced the genome of a historical prototype strain (L2/434/Bu) and a clinical isolate (E/CS88), before and after one-year of serial in vitro passaging (up to 3500 bacterial generations). We observed a slow adaptation of C. trachomatis to the in vitro environment, which was essentially governed by four mutations for L2/434/Bu and solely one mutation for E/CS88, corresponding to estimated mutation rates from 3.84 × 10−10 to 1.10 × 10−9 mutations per base pair per generation. In a speculative basis, the mutations likely conferred selective advantage as: (i) mathematical modeling showed that selective advantage is mandatory for frequency increase of a mutated clone; (ii) transversions and non-synonymous mutations were overrepresented; (iii) two non-synonymous mutations affected the genes CTL0084 and CTL0610, encoding a putative transferase and a protein likely implicated in transcription regulation respectively, which are families known to be highly prone to undergone laboratory-derived advantageous mutations in other bacteria; and (iv) the mutation for E/CS88 is located likely in the regulatory region of a virulence gene (CT115/incD) believed to play a role in subverting the host cell machinery. Nevertheless, we found no significant differences in the growth rate, plasmid load, and attachment/entry rate, between strains before and after their long-term laboratory propagation. Of note, from the mixture of clones in E/CS88 initial population, an inactivating mutation in the virulence gene CT135 evolved to 100% prevalence, unequivocally indicating that this gene is superfluous for C. trachomatis survival in vitro. Globally, C. trachomatis revealed a slow in vitro adaptation that only modestly modifies the in vivo-derived genomic evolutionary landscape.