Parasite and bacterium illustrate convergent evolution: Both hijack cells' 'post office'

Dec 13, 2010

The protozoan parasite Toxoplasma gondii and the pathogenic bacterium Chlamydia trachomatis exemplify convergent evolution, the development of a similar biological trait in unrelated lineages, according to research presented today at the American Society of Cell Biology's 50th Annual Meeting in Philadelphia.

The biological trait shared by the two pathogens is their modus operandi – how they operate inside human host cells to reproduce themselves, said scientists at the Johns Hopkins Bloomberg School of Public Health, working with researchers at the University of Maryland Dental School and the University of Zurich in Switzerland.

Both T. gondii and hijack their host cells' Golgi apparatus, the "post office of the cell" because it packs up and dispatches cellular cargoes such as lipids in sealed vacuoles. After taking over the Golgi, both reorganize the organelle into mini-stacks conveniently aligned just outside each invader's hiding place in the cell.

In addition to being an example of convergent , the pathogens' predatory similarity is a possible clue for improving therapies to contain two of the most common infections on earth, said Julia Romano, Ph.D., and Isabelle Coppens, Ph.D.

The research that lead to the discovery of T. gondii and Chlamydia's similar mode of action was prompted by a study on how Toxoplasma secures a nutrient supply inside an infected host. In that National Institutes of Health supported study, scientists noticed a strong parallel with chlamydial infection that had not been suspected since protozoa and bacteria stem from distant evolutionary branches.

Romano and Coppens investigated Toxoplasma-infected host cells to determine how the parasite hijacks lipids named ceramides and found that the protozoan hid from the host's immune system by living inside its own capsule, parasitophorous vacuole (PV). They then determined that the protozoan was able to grab nutrients without exposing itself, because it had located its PV near the hub of the cell's cargo system, the pericentriolar region, and thus close to the Golgi. Within 32 hours of infecting a , the protozoan had sliced the Golgi into fragmented mini-disks and was ingesting intact vacuoles containing ceramides through its PV membrane.

The remodeled Golgi, the PV's location in the pericentriolar region, and the efficient capture of the host's sphingolipid supply reminded the researchers of infection by C. trachomatis, which causes the most frequently reported sexually transmitted disease in the U.S. To test the parallel, the researchers co-infected mammalian cells with T. gondii and C. trachomatis and then observed the two pathogens' quickly dividing the Golgi between them. The two disparate pathogens' distributing the fragments of the organelle equally indicates a common evolutionary strategy.

According to the U.S. Centers for Disease Control (CDC), 1.2 million cases of C. trachomatis infection were reported during 2008 in the U.S. "Silent," untreated C. trachomatis infections can cause infertility in women. Spread by infected meat, Toxoplasmosis is the third leading cause of death attributed to food borne illness.

Explore further: Mycologist promotes agarikon as a possibility to counter growing antibiotic resistance

Provided by American Society for Cell Biology

5 /5 (1 vote)

Related Stories

How Toxoplasma gondii gets noticed

Jan 19, 2009

Researchers provide insight into how Toxoplasma gondii, a common parasite of people and other animals, triggers an immune response in its host. The report will appear online on January 19th in The Journal of Experimental Medicine. ...

Toxoplasmosis infection trick revealed by scientists

May 10, 2007

Toxoplasmosis is a parasitic disease, primarily carried by cats. It is transmitted to humans by eating undercooked meat or through contact with cat faeces. It is particularly dangerous for pregnant women, whose foetuses can ...

Study: How an internal organelle doubles

Nov 07, 2005

Yale University scientists have found a mechanism that regulates the way an internal organelle, the Golgi apparatus, duplicates as cells prepare to divide.

Recommended for you

YEATS protein potential therapeutic target for cancer

Oct 23, 2014

Federal Express and UPS are no match for the human body when it comes to distribution. There exists in cancer biology an impressive packaging and delivery system that influences whether your body will develop cancer or not.

Precise and programmable biological circuits

Oct 23, 2014

A team led by ETH professor Yaakov Benenson has developed several new components for biological circuits. These components are key building blocks for constructing precisely functioning and programmable bio-computers.

User comments : 0