Adaptive laboratory evolution of a thermophile toward a reduced growth temperature optimum

Maria Lehmann; Christoph Prohaska; Benjamin Zeldes; Anja Poehlein; Rolf Daniel; Mirko Basen

doi:10.3389/fmicb.2023.1265216

Adaptive laboratory evolution of a thermophile toward a reduced growth temperature optimum

Front Microbiol. 2023 Oct 12:14:1265216. doi: 10.3389/fmicb.2023.1265216. eCollection 2023.

Authors

Maria Lehmann^#¹, Christoph Prohaska^#¹, Benjamin Zeldes¹, Anja Poehlein², Rolf Daniel², Mirko Basen¹

Affiliations

¹ Department of Microbiology, Institute of Biological Sciences, University of Rostock, Rostock, Germany.
² Genomic and Applied Microbiology and Göttingen Genomics Laboratory, Georg-August University, Göttingen, Germany.

^# Contributed equally.

Abstract

Thermophily is an ancient trait among microorganisms. The molecular principles to sustain high temperatures, however, are often described as adaptations, somewhat implying that they evolved from a non-thermophilic background and that thermophiles, i.e., organisms with growth temperature optima (T_OPT) above 45°C, evolved from mesophilic organisms (T_OPT 25-45°C). On the contrary, it has also been argued that LUCA, the last universal common ancestor of Bacteria and Archaea, may have been a thermophile, and mesophily is the derived trait. In this study, we took an experimental approach toward the evolution of a mesophile from a thermophile. We selected the acetogenic bacterium T. kivui (T_OPT 66°C) since acetogenesis is considered ancient physiology and cultivated it at suboptimal low temperatures. We found that the lowest possible growth temperature (T_MIN) under the chosen conditions was 39°C. The bacterium was subsequently subjected to adaptive laboratory evolution (ALE) by serial transfer at 45°C. Interestingly, after 67 transfers (approximately 180 generations), the adapted strain Adpt45_67 did not grow better at 45°C, but a shift in the T_OPT to 60°C was observed. Growth at 45°C was accompanied by a change in the morphology as shorter, thicker cells were observed that partially occurred in chains. While the proportion of short-chain fatty acids increased at 50°C vs. 66°C in both strains, Adpt45_67 also showed a significantly increased proportion of plasmalogens. The genome analysis revealed 67 SNPs compared to the type strain, among these mutations in transcriptional regulators and in the cAMP binding protein. Ultimately, the molecular basis of the adaptation of T. kivui to a lower T_OPT remains to be elucidated. The observed change in phenotype is the first experimental step toward the evolution of thermophiles growing at colder temperatures and toward a better understanding of the cold adaptation of thermophiles on early Earth.

Keywords: Thermoanaerobacter kivui; acetogens; adaptive laboratory evolution; cold adaptation; origin of life; thermophiles.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This study was funded by a grant from VolkswagenStiftung (Volkswagen Foundation, A123851) in the Experiment! program (exploratory phase). The authors acknowledge financial support from the Deutsche Forschungsgemeinschaft and Universität Rostock within the funding program Open Access Publishing.