Breakthrough Enables Manipulation of the Chlamydia Genome

It is an obligate intracellular bacterium, which has a complex developmental cycle that takes place in a specialized host cell cytoplasmic vacuole known as an inclusion. The extracellular infectious elementary body (EB) is an infectious, electron-dense structure that, following host cell infection, differentiates into a noninfectious replicative form known as a reticulate body (RB).

In a paper published in the September 22, 2011, online edition of the journal PLoS Pathogens investigators at the University of Southampton (United Kingdom) and Ben Gurion University of the Negev (Be’er Sheva, Israel) reported that they had achieved a significant breakthrough in accessing the chlamydial genome.

This feat was accomplished by isolating penicillin resistant Chlamydia that were then treated with calcium chloride (CaCl2). Penicillin prevented the maturation of RBs into EBs. Instead, the RBs failed to divide although DNA replication continued. The investigators exploited these observations to develop a transformation protocol based on expression of beta-lactamase. They constructed a vector that carried both the chlamydial endogenous plasmid and a replication plasmid of E. coli origin so that the vector could shuttle between these two bacterial recipients. Proof of the method was obtained by insertion of the gene for a fluorescent protein into C. trachomatis, which identified chlamydial-infected cells by making them glow green.

"This is a very significant advance in the study of Chlamydia and we are proud to be the first people to achieve this,” said senior author Dr. Ian Clarke, professor of molecular microbiology at the University of Southampton. “Previously people have been unable to study chlamydial genetics, and this has created a barrier to the comprehensive study of this disease. We, together with our colleagues in Israel, discovered that by treating the Chlamydia with calcium ions we were able to introduce a piece of foreign DNA. This will open up the field of Chlamydia research and will enable a better understanding of chlamydial genetics. It could lead to the development of new approaches to chlamydial vaccines and therapeutic interventions.”

Related Links:
University of Southampton
Ben Gurion University of the Negev