Phenotyping Thermal Responses of Yeasts and Yeast-like Microorganisms at the Individual and Population Levels: Proof-of-Concept, Development and Application of an Experimental Framework to a Plant Pathogen
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Deciphering the responses of microbial populations to spatiotemporal changes in their thermal environment is instrumental in improving our understanding of their eco-evolutionary dynamics. Recent studies have shown that current phenotyping protocols do not adequately address all dimensions of phenotype expression. Therefore, these methods can give biased assessments of sensitivity to temperature, leading to misunderstandings concerning the ecological processes underlying thermal plasticity. We describe here a new robust and versatile experimental framework for the accurate investigation of thermal performance and phenotypic diversity in yeasts and yeast-like microorganisms, at the individual and population levels. In addition to proof-of-concept, the application of this framework to the fungal wheat pathogen Zymoseptoria tritici resulted in detailed characterisations for this yeast-like microorganism of (i) the patterns of temperature-dependent changes in performance for four fitness traits; (ii) the consistency in thermal sensitivity rankings of strains between in planta and in vitro growth assessments; (iii) significant interindividual variation in thermal responses, with four principal thermotypes detected in a sample of 66 strains; and (iv) the ecological consequences of this diversity for population-level processes through pairwise competition experiments highlighting temperature-dependent outcomes. These findings extend our knowledge and ability to quantify and categorise the phenotypic heterogeneity of thermal responses. As such, they lay the foundations for further studies elucidating local adaptation patterns and the effects of temperature variations on eco-evolutionary and epidemiological processes.
KeywordsPhenotyping Responses to temperature Thermal performance curve Diversity metrics Yeast-like microorganisms Zymoseptoria tritici
We would like to thank Alain Fortineau for designing the experimental setup used for monitoring liquid medium and wheat leaf temperatures; Marc-Henri Lebrun for kindly providing the GFP-transformed strain of Z. tritici; Laurent Falchetto, Bernard Gesret, Henriette Goyeau, Marc Leconte and Ivan Sache for their help in sampling the French Z. tritici populations used in this study; Ons El Kamel for her assistance in collecting in planta epidemiological data and Bérengère Dalmais for providing support for fluorescence microscopy.
A.-L. B., M.C. and F.S. conceived and designed the study. Experiments were performed by A.-L. B., with the help of G.D. for method development and J.L. for in vitro growth monitoring of the French Z. tritici populations. A.-L. B. performed data analyses. A.-L. B., M.C. and F.S. wrote the manuscript.
This work was supported by a grant from the French National Research Agency (ANR) as part of the ‘Investissements d’Avenir’ programme (SEPTOVAR project; LabEx BASC; ANR-11-LABX-0034) and by a PhD fellowship from the French Ministry of Education and Research (MESR) awarded to A.-L. B.
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Conflict of Interest
The authors declare that they have no conflict of interest.
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