Some of the most important discoveries in biology arrive by accident. In a laboratory at the University of Exeter, a researcher was testing the killer fungus Candida auris against antifungal drugs and left the plates incubating longer than the protocol required. When they returned, something impossible had happened: cells exposed to drug concentrations that should have killed them were growing.
The finding, reported this week in Nature Communications by a team from Exeter and City St George's, University of London, rewrites part of what we know about drug resistance. The survivors had not acquired the mutations everyone expected. Instead, they had copied their entire genome, multiple times. Whole-genome duplication turned out to be a survival strategy: a brute-force trick that gives the fungus extra rolls of the evolutionary dice.
What the fungus actually did
To see why the trick matters, it helps to know how antifungal drugs work. Drugs in the echinocandin class attack the enzymes that build the fungal cell wall. Without a functioning wall, the fungus dies by shriveling, rupturing, or failing to grow. The standard story of resistance is that a mutation alters the drug's target enzyme, and in C. auris that usually means changes to the FKS1 or FKS2 genes. This time, sequencing found none of those.
What it found instead was a genome copied wholesale. The surviving cells carried multiple versions of their entire genetic blueprint, and the fast-growing survivors carried a wide range of mutations in a gene called CRZ1, nicknamed "Crazy-one," which governs cell wall synthesis. Follow-up tests confirmed the pattern: CRZ1 mutants grew rapidly, and their cell walls appeared unaffected by the drugs. The fungus had rebuilt its wall using instructions written by its own spare genome copies.
The fungus did not crack the drug. It rebuilt its entire cell wall from spare blueprints it copied itself.
Bet-hedging, or why two populations beat one
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The lab cultures revealed something else: the survivors were not uniform. Some grew slowly, others grew rapidly. The team calls this bet-hedging. Rather than gambling everything on one winning mutation, the fungus spawns multiple subpopulations that pursue different survival strategies at once. The slow growers may simply ride out the drug; the fast growers carry the CRZ1 mutations that let them thrive despite it.
Bet-hedging is not new in nature. Plants stagger seed germination across years; bacteria generate persister cells that tolerate antibiotics. But documented, whole-genome-level bet-hedging in a deadly human pathogen is new, and it suggests fungal infections may be more complicated than the single-strain model used in most laboratory tests. Multiple populations may coexist during an actual infection, each responding to treatment differently.
Why this changes how we treat it
Candida Auris, by the Numbers
The threat profile of a fungus that innovates with its own genome.
Note: Figures from the University of Exeter and City St George's, University of London study.
Candida auris is not an obscure threat. First described in 2008, its origins remain a mystery, but it has since been reported on every continent, in more than 60 countries. The World Health Organization placed it on its critical priority fungal pathogens list. It is rare in the general population but a nightmare in intensive care units, where it clings to skin and equipment, spreads person to person, and resists eradication. If it enters a vulnerable patient's bloodstream, the death rate is 45 percent.
Outbreaks are disruptive and expensive. One UK intensive care unit had to close and undergo complete refurbishment to stop an outbreak; another outbreak was estimated to cost 1 million pounds to control. The antifungal arsenal is thin, with far fewer new drugs in development than for bacteria, which makes every resistance mechanism a bigger problem than it would otherwise be.
The response under study is combination therapy. The Exeter-led, UKRI-funded Fungi-CARE program, run with City St George's, is exploring whether hitting the fungus with antifungal drugs in combination can close the escape routes that a single drug leaves open. The logic is straightforward: bet-hedging works against one selection pressure. Two or more pressures, applied together, should make it much harder for any single subpopulation to cover them all.
Resistance is not just about mutations anymore
The broader lesson reaches beyond one fungus. A separate analysis in Nature Communications, from a different group, recently showed that segmental genome duplications and even extra whole chromosomes also help C. auris resist drugs, pointing to the same theme: genome plasticity, not just point mutations, drives antifungal resistance. For years the field treated drug-target mutations as the main story. That picture is getting more complicated, and more interesting.
The discovery is also a quiet advertisement for the tools that made it possible. None of this would have been visible without cheap, fast genome sequencing, which has turned evolution from a story told in fossils into something you can watch happen on a petri dish in days. The over-incubated plate was an accident. Reading the survivors' entire genome and seeing exactly what changed was technology.
For now, the practical message is caution and urgency. Fungal pathogens are innovating with their own genomes in ways we are only beginning to document, the drug pipeline is thin, and the organisms are, as the researchers put it, carrying a Swiss Army knife of evolutionary options. In the arms race between drugs and pathogens, the pathogens are running a surprisingly sophisticated research operation.
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