Pombert’s Paper on Discovery About Pathogen’s Evolution in PNAS

Jean-Francois Pombert, IIT assistant professor of biology, and his international collaborators have discovered new information about the evolution of pathogens known as Microsporidia: that their polar tube and mitochondrion coexisted for a time. While their modes of infection are relatively well understood, how these came to be were unclear, and the current results shed light on the matter. A paper about their research, “Evolution of a morphological novelty occurred before genome compaction in a lineage of extreme parasites” was published in the Proceedings of the National Academy of Sciences (PNAS) October 13, 2014.

Microsporidia are food/waterborne pathogens of economic, environmental and medical importance, causing various and sometimes lethal afflictions in human patients including diarrhea, keratoconjunctivitis (inflammation of the eye), myositis (inflammation of muscles), and encephalitis (inflammation of the brain). These highly derived fungi possess a unique infection apparatus called the polar tube, a molecular contraption that ejects rapidly from the spores to pierce and initiate the invasion of the adjacent cells. Like many intracellular pathogens, Microsporidia are tiny vampires incapable of oxygenic respiration (they lack mitochondria) and must therefore steal energy from their hosts to survive. Little is known about the origins of these parasites, however.

In their paper, Pombert and his collaborators report the first example of a microsporidia with a polar tube and a functional mitochondrion. Their results indicate that the rise of the polar tube occurred before the degradation of the mitochondrion and that the two coexisted for a time. This means that the infection mechanism was not developed in response to a severe metabolic deficiency but rather that the loss of oxygenic respiration was made possible by the efficient modes of invasions provided by the fully developed polar tube.

Pombert served as the genomics expert on the project. His collaborators included Karen L. Haag (Federal University of Rio Grande do Sul, Brazil), Timothy Y. James (University of Michigan), Ronny Larsson (University of Lund, Sweden), Tobias M. M. Shaer (Basel University, Switzerland), Dominik Refardt (Zurich University of Applied Sciences, Switzerland), and Dieter Ebert (Basel University, Switzerland)