Algal Ancestor Shows How Deadly Pathogens Proliferate

Long ago, when life on our planet was in its infancy, a group of small single-celled algae floating in the vast prehistoric ocean swam freely by beating whip-like tails, or flagella. Now, over 800 million years later, these organisms have evolved into parasites called Apicomplexa, but are better known as the parasites that cause Malaria and Toxoplasmosis—serious diseases that infect millions of people every year, particularly in the developing world.

Now their algal past in the ocean may be the key to stopping the spread of these diseases, and is explored in the recent PLOS Biology article by Francia et al, and also in the accompanying synopsis by Stephanie Huang.

Professor Boris Striepen and colleagues from the University of Georgia explain in this paper how an important structure inside these parasitic cells, which evolved from the algal ancestor millions of years ago, allows the cells to replicate and spread inside their hosts. Their research may lead to new therapies to halt these deadly pathogens before they cause disease.

In their study, the researchers demonstrate that during the process of replication, and spreading the infection throughout the body, the parasite cell loads genetic material into its daughter cells via a strand of fiber that connects the two. By altering the genes for the components of this fiber in the laboratory, the researchers discovered that they could prevent parasite replication, rendering the parasite essentially harmless.

“These altered parasites can initially infect cells, but once we turn off the fiber genes, they cannot create new daughter cells and spread,” said Maria Francia, lead author of the study. “Since it cannot replicate, the parasite eventually dies without causing serious harm.”

This replication fiber appears to have evolved from the flagellum that enabled ancient algae to swim.

“This was a surprising finding,” said Boris Striepen. “These parasites no longer use flagella to swim, but they have apparently now repurposed this machinery to organize the assembly of an invasive cell”.

The findings of this new research are also the topic of an accompanying PLOS Biology synopsis, by Stephanie Huang, which highlights the importance of the research with regards to the current difficulties in treating malaria and toxoplasmosis. First, the parasites are eukaryotic and thus more similar to human cells than bacterial pathogens, making it difficult to find treatments that kill the parasite without harming human host cells. Second, the parasite cells reside within human host cells for much of their life cycle, evading detection by the host’s immune system.

“It is extremely important to understand the evolution of different organisms, but especially the evolution of pathogens,” Striepen says. “The analysis of their evolution produces important opportunities to develop treatments, but it also helps us understand the basic structures of the pathogens that we must fight.”

Maria E. Francia,, Carly N. Jordan,, Jay D. Patel,, Lilach Sheiner,, Jessica L. Demerly,, Justin D. Fellows,, Jessica Cruz de Leon,, Naomi S. Morrissette,, Jean-François Dubremetz,, & Boris Striepen (2012). Cell Division in Apicomplexan Parasites Is Organized by a Homolog of the Striated Rootlet Fiber of Algal Flagella PLOS Biology : 10.1371/journal.pbio.1001444