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Updated: Jul 12, 2025
Assay for Adhesion and Agar Invasion in S. cerevisiae
Published on: November 8, 2006
Selection on plastic adherence leads to hyper-multicellular strains and incidental virulence in the budding yeast
Luke I Ekdahl1, Juliana A Salcedo1, Matthew M Dungan1
1Department of Biology, College of William and Mary, Williamsburg, United States.
Abstract:
Many disease-causing microbes are not obligate pathogens; rather, they are environmental microbes taking advantage of an ecological opportunity. The existence of microbes whose life cycle does not require a host and are not normally pathogenic, yet are well-suited to host exploitation, is an evolutionary puzzle. One hypothesis posits that selection in the environment may favor traits that incidentally lead to pathogenicity and virulence, or serve as pre-adaptations for survival in a host. An example of such a trait is surface adherence. To experimentally test the idea of 'accidental virulence', replicate populations of Saccharomyces cerevisiae were evolved to attach to a plastic bead for hundreds of generations. Along with plastic adherence, two multicellular phenotypes- biofilm formation and flor formation- increased; another phenotype, pseudohyphal growth, responded to the nutrient limitation. Thus, experimental selection led to the evolution of highly-adherent, hyper-multicellular strains. Wax moth larvae injected with evolved hyper-multicellular strains were significantly more likely to die than those injected with evolved non-multicellular strains. Hence, selection on plastic adherence incidentally led to the evolution of enhanced multicellularity and increased virulence. Our results support the idea that selection for a trait beneficial in the open environment can inadvertently generate opportunistic, 'accidental' pathogens.
Insights
Environmental microbes can become pathogens by evolving traits like surface adherence. This study shows selection for adherence in yeast incidentally increased multicellularity and virulence, supporting the concept of "accidental pathogens".
Area of Science:
- Evolutionary biology
- Microbiology
- Pathogenesis
Background:
- Many pathogens originate from environmental microbes, not obligate pathogens.
- The evolution of host-independent microbes that become pathogenic presents an evolutionary puzzle.
- Surface adherence is a trait potentially favoring environmental survival and host exploitation.
Purpose of the Study:
- To experimentally test the hypothesis of 'accidental virulence'.
- To investigate if selection for a non-pathogenic trait (surface adherence) can lead to increased pathogenicity.
- To explore the link between environmental adaptation and opportunistic pathogenicity.
Main Methods:
- Experimental evolution of *Saccharomyces cerevisiae* populations for plastic adherence over hundreds of generations.
- Quantification of multicellular phenotypes (biofilm, flor, pseudohyphal growth) in evolved strains.
- Virulence testing using wax moth larvae injected with evolved yeast strains.
Main Results:
- Experimental evolution significantly increased plastic adherence and multicellular phenotypes (biofilm, flor formation).
- Hyper-multicellular strains evolved from selection for adherence showed increased virulence.
- Wax moth larvae injected with hyper-multicellular strains had higher mortality rates compared to controls.
Conclusions:
- Selection for surface adherence in an environmental context can incidentally lead to increased virulence.
- This study supports the concept of 'accidental pathogens' arising from environmental adaptations.
- Environmental selection pressures can inadvertently pre-adapt microbes for host exploitation and disease.
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