A common mechanism involving the TORC1 pathway can lead to amphotericin B-persistence in biofilm and planktonic Saccharomyces cerevisiae populations.

Rasmus Bojsen,Anders Folkesson,David Gresham,Birgitte Regenberg

doi:10.1038/srep21874

Rasmus Bojsen, Anders Folkesson + Show 2 more

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https://doi.org/10.1038/srep21874

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Abstract

Fungal infections are an increasing clinical problem. Decreased treatment effectiveness is associated with biofilm formation and drug recalcitrance is thought to be biofilm specific. However, no systematic investigations have tested whether resistance mechanisms are shared between biofilm and planktonic populations. We performed multiplexed barcode sequencing (Bar-seq) screening of a pooled collection of gene-deletion mutants cultivated as biofilm and planktonic cells. Screening for resistance to the ergosterol-targeting fungicide amphotericin B (AmB) revealed that the two growth modes had significant overlap in AmB-persistent mutants. Mutants defective in sterol metabolism, ribosome biosynthesis, and the TORC1 and Ras pathways showed increased persistence when treated with AmB. The ras1, ras2 and tor1 mutants had a high-persister phenotype similar to wild-type biofilm and planktonic cells exposed to the TORC1 pathway inhibitor rapamycin. Inhibition of TORC1 with rapamycin also increased the proportion of persisters in Candida albicans and Candida glabrata. We propose that decreased TORC1-mediated induction of ribosome biosynthesis via Ras can lead to formation of AmB-persister cells regardless of whether the cells are in planktonic or biofilm growth mode. Identification of common pathways leading to growth mode-independent persister formation is important for developing novel strategies for treating fungal infections.

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Biofilms formed by C. albicans, survive amphotericin B (AmB) treatment by the formation of persister cells that are characterized by noninherited resistance[12]
We investigated if AmB resistance was noninherited in our S. cerevisiae biofilm model by treating 24-hour biofilms with AmB and re-treating new biofilms formed by persisters with AmB for a total of three treatment cycles (Fig. 1a)

Summary

Introduction

Users may download and print one copy of any publication from the public portal for the purpose of private study or research. The ras[1], ras[2] and tor[1] mutants had a high-persister phenotype similar to wild-type biofilm and planktonic cells exposed to the TORC1 pathway inhibitor rapamycin. We propose that decreased TORC1-mediated induction of ribosome biosynthesis via Ras can lead to formation of AmB-persister cells regardless of whether the cells are in planktonic or biofilm growth mode. The polyene drug amphotericin B (AmB) targets ergosterol in the cell membrane and forms pores that rapidly lyse cells[5] These fungicidal properties and broad spectrum of activity have made AmB the preferred agent for treatment of severe mycosis since its introduction in the late 1950s. Less is known about persistence in yeast, histone deacetylases[14] and superoxide dismutases[15] are suggested to be involved

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