Fungus, Family Trees, and Fatal Disease

What’s in a name? For scientists, a lot—figuring out the different species in the tree of life can help in conservation efforts. But a new study by an international group of researchers including the Field Museum illuminating different yeast species could be crucial in AIDS treatments.

Field Museum scientist Thorsten Lumbsch, PhD, and an international team led by Teun Boekhout from the Netherlands have discovered that two species of yeast as they’re currently classified—Cryptococcus neoformans and Crytopcoccus gattii—actually contain at least seven different species. And one of those species, C. neoformans, is the number-one killer of AIDS patients in sub-Saharan Africa. Now that scientists know that this species is split even further into different organisms, it may be possible to create life-saving medical treatments to target those specific yeasts.

“It’s pure basic research. We’re looking at different species of yeast and figuring out how they’re related, how they’re different. But this basic research will let other scientists do applied research that could save lives,” said Lumbsch.

Yeasts, like molds and mushrooms, are fungi—organisms separate from plants, animals, and bacteria. Some species of yeast, including the ones in this study, can cause infections. Normally, our immune systems kill off these yeasts, but people with compromised immune systems like AIDS patients and organ donation recipients are left vulnerable. The fungus can grow inside their bodies, destroying their brains and lungs.

“More people die of Cryptococcus than all other STDs combined in sub-Saharan Africa. Almost as many people die because of this yeast than from malaria,” said Lumbsch.

Lumbsch’s colleagues in Europe took DNA samples from the yeasts (even though fungi are radically different life forms from us, the building blocks of their DNA are identical to ours). They then sequenced the DNA, creating a “list” of the genetic code that makes up the yeasts. Once The Field’s Lumbsch got the DNA sequences, he uploaded them into a computer program that creates evolutionary trees—basically, family trees showing how similar the specimens’ DNA are to each other. In the hundreds of trials Lumbsch ran, the program kept coming back with the same answer: instead of the yeast DNA samples representing two species, they actually formed seven separate species.

So where we once thought there were two species of yeast, there are now seven. But how can this information make a difference?

“In general, fungi are very difficult to treat—the medicines that kill them harm our cells too,” says Lumbsch. “If we have a better idea of what kind of yeast is causing these infections, we can develop better treatments.”