Single-cell parasites co-opt 'ready-made' genes from host

Part of a group of parasitic microbes called microsporidia, Encephalitozoon hellem and Encephalitozoon romaleae are related to fungi and are commonly found in the intestines of vertebrates. In humans, they are associated with people with immune deficiencies.

The research team identified six genes in these parasites that were not found in any other microsporidian. Rather than the slow process of inheriting individual genes, E. hellem and E. romaleae have acquired a suite of genes that produce folate, a form of folic acid that helps cell division and growth.

Details are published this week in the online journal PNAS Early Edition.

"With their tiny, reduced genomes, microsporidia are models for gene loss," says lead author Patrick Keeling, a professor in UBC's Dept. of Botany.

"These parasites have undergone massive genome reductions and are literally infection machines -- they only kept genes that are essential for survival."

"But here we found two species have actually acquired new genes that work together to make an essential nutrient that the parasites would otherwise have to steal from their host -- opening up new tissues or even new hosts as targets for infection," says Keeling, director of the Centre for Microbial Diversity and Evolution and a member of Beaty Biodiversity Research Centre at UBC.

The process of horizontal gene transfer -- the ability to acquire ready-made genes with specific functions from foreign genomes -- is an important but often overlooked mechanism of evolution, according to Keeling. "It helps explain the relatively rapid evolution of these tiny organisms and their ability to infect and live off of a wide variety of hosts."