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Modern genetics vs. ancient frog-killing fungus
Date:10/14/2008

ement in the killing process.

Because the fungus is so ancient, it differs wildly from most species scientists study, and many of its genes have unknown functions. To combat these unknowns, Rosenblum and her colleagues sequenced Bd's entire genome and compared the expression of genes in two phases of the fungus's life - the zoospore and sporangia stages.

The zoospore stage is the earliest form of the fungus when it is just a single cell swimming around looking for a host on which to grow. Once it embeds itself into an amphibian's skin, it grows into a more complex form called the sporangia stage. In this stage, Bd grows on the keratin in the frog's skin, creating more zoospores to spread the disease and often killing the host.

By looking at which genes are turned on when the fungus actively is destroying the skin, but are turned off when the fungus is doing little more than swimming around, scientists hoped to find candidates for genes responsible for both spreading the fungus and killing the frogs.

"We care about the zoospores because that's the stage it is swimming around and finding frogs to infect," said Rosenblum. "And we care about the sporangia stage because that's when Bd is actually killing the frogs."

The study flags many genes as potentially important, but Rosenblum identifies one family as particularly interesting. The family of genes in question, known as fungalysin metallopeptidase, has only one or few representative in similar fungi that do not kill frogs. But in this deadly fungus, genes in the family appear 29 times. Additionally, the genes generally are turned on when the fungus is infecting frogs, but turned off in the zoospore stage.

Although this gene family is an excellent candidate for the pathogen's killing ability, it is not certain. Discovering for sure which genes raise or lower the fungi's killing ability is a long process, partly because the fungus is so far removed from other organi
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Contact: Ken Kingery
kkingery@uidaho.edu
208-885-9156
University of Idaho
Source:Eurekalert

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