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Published on: February 14, 2018
Cross-feeding affects the target of resistance evolution to an antifungal drug
Romain Durand1,2,3,4,5, Jordan Jalbert-Ross1,2,3,4, Anna Fijarczyk1,2,3,4,5
1Département de Biochimie, de Microbiologie et de Bio-informatique, Faculté des Sciences et de Génie, Université Laval, Canada.
Abstract:
Pathogenic fungi are a cause of growing concern. Developing an efficient and safe antifungal is challenging because of the similar biological properties of fungal and host cells. Consequently, there is an urgent need to better understand the mechanisms underlying antifungal resistance to prolong the efficacy of current molecules. A major step in this direction would be to be able to predict or even prevent the acquisition of resistance. We leverage the power of experimental evolution to quantify the diversity of paths to resistance to the antifungal 5-fluorocytosine (5-FC), commercially known as flucytosine. We generated hundreds of independent 5-FC resistant mutants derived from two genetic backgrounds from wild isolates of Saccharomyces cerevisiae. Through automated pin-spotting, whole-genome and amplicon sequencing, we identified the most likely causes of resistance for most strains. Approximately a third of all resistant mutants evolved resistance through a pleiotropic drug response, a potentially novel mechanism in response to 5-FC, marked by cross-resistance to fluconazole. These cross-resistant mutants are characterized by a loss of respiration and a strong tradeoff in drug-free media. For the majority of the remaining two thirds, resistance was acquired through loss-of-function mutations in FUR1, which encodes an important enzyme in the metabolism of 5-FC. We describe conditions in which mutations affecting this particular step of the metabolic pathway are favored over known resistance mutations affecting a step upstream, such as the well-known target cytosine deaminase encoded by FCY1. This observation suggests that ecological interactions may dictate the identity of resistance hotspots.
Insights
Understanding antifungal resistance is crucial. Experimental evolution revealed novel resistance mechanisms to 5-fluorocytosine (5-FC) in yeast, including a pleiotropic drug response and mutations in FUR1, offering insights into preventing drug resistance.
Area of Science:
- Mycology
- Antimicrobial Resistance
- Evolutionary Biology
Background:
- Pathogenic fungi pose a growing health concern, necessitating effective antifungal treatments.
- Developing new antifungals is difficult due to similarities between fungal and host cells.
- Understanding antifungal resistance mechanisms is vital to prolong the efficacy of existing drugs.
Purpose of the Study:
- To investigate the diverse evolutionary pathways leading to resistance against the antifungal 5-fluorocytosine (5-FC).
- To identify genetic mutations and cellular mechanisms conferring 5-FC resistance in Saccharomyces cerevisiae.
- To explore potential novel mechanisms of antifungal resistance and their implications for treatment strategies.
Main Methods:
- Utilizing experimental evolution to generate hundreds of independent 5-FC resistant mutants from two distinct Saccharomyces cerevisiae genetic backgrounds.
- Employing automated pin-spotting for high-throughput screening of resistant mutants.
- Performing whole-genome and amplicon sequencing to identify the genetic basis of resistance.
Main Results:
- Approximately one-third of resistant mutants exhibited a pleiotropic drug response, showing cross-resistance to fluconazole, characterized by loss of respiration and fitness trade-offs.
- The majority of remaining mutants acquired resistance through loss-of-function mutations in FUR1, an enzyme critical for 5-FC metabolism.
- Identified conditions favoring mutations in FUR1 over upstream targets like FCY1, suggesting ecological factors influence resistance hotspots.
Conclusions:
- Experimental evolution is a powerful tool for dissecting antifungal resistance mechanisms.
- A pleiotropic drug response represents a potentially novel mechanism of 5-FC resistance in yeast.
- Ecological interactions may play a significant role in determining the specific genetic pathways of antifungal resistance.
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