Its name is Batrachochytrium dendrobatidis (Bd). It is a “chytrid” fungus that lives on keratin, a type of protein found in the skin of amphibians, and is particularly deadly for certain species of frogs. A summary of key findings from the 2004 Global Amphibian Assessment states that 43 percent of all frog species are declining in population, with less than 1 percent showing increases. Although there are many reasons for frog decline, including climate change and habitat loss, Bd seriously is affecting a growing number of species.
“This fungus is really bizarre,” said Erica Bree Rosenblum, assistant professor of biological sciences at the University of Idaho and lead author of the study published this week in the Proceedings of the National Academy of Sciences (PNAS). “It’s a member of an group of ancient fungi that are at least a half billion years old. But it only recently began killing amphibians and unequivocally is responsible for a lot of the catastrophic frog die-offs during the past decade.”
Previous studies have shown that once Bd is introduced to a habitat, up to 50 percent of amphibian species and 80 percent of individuals may die within one year. The fungus has been studied for the past decade, yet scientists still do not know much about how Bd kills its host.
However, Rosenblum’s new paper brings scientists one step closer to solving the mystery. The study uses some of the most advanced genetic technology available in an attempt to understand how the fungus works at the most basic level. It identifies several gene families for future study, including one strong candidate that may be a key element 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 actually is 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 organisms in the evolutionary tree.
“This fungus is strange and different, partly because it is so ancient,” said Rosenblum. “One of the really amazing and wonderful things about this genetic technology is that we can take something we don’t know anything about, sequence its whole genome, look at what each gene is doing in different life stages, and learn a tremendous amount about the organism.”
Rosenblum and her team will continue their quest to stop Bd from killing off frog species in several ways. They currently are comparing active genes in Bd grown on frog skin to Bd grown in a test tube without exposure to keratin. Also, they plan to sequence genomes from different strains of Bd that kill less efficiently, or other, similar fungi that don’t kill amphibians at all.
They also will study the parasite from the other side of the coin – the frog’s point of view. By comparing different species of frogs, some of which are not killed by Bd, they hope to discover what genes make different species more or less susceptible to the fungus.
“The strength of these studies is the collaboration of ecologists and disease biologists,” said Rosenblum. “We are not just choosing one factor to study. Looking at absolutely every gene in the genome is now a financially and practically feasible thing to do.”
Rosenblum’s research is featured in the October 13-17 edition of PNAS Online Early Edition, article #08-04173. Read it online at http://www.pnas.org/early/recent
A Map of the Cell’s Power Station
18.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
On the way to developing a new active ingredient against chronic infections
18.08.2017 | Deutsches Zentrum für Infektionsforschung
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences