Global patterns of taxonomic and functional diversity in hot springs microbiomes

A reformulation of the metabolic theory of ecology has been proposed based on a derivation of the Eyring-Polanyi equation, leading to a reduced model with the form of a power-law with exponential cut-off (PLECO). Moreover, the recent integration of this new model and metagenomic DNA sequencing theory has led to the hypothesis that, given that temperature affects cell size and assemblage abundance, it should also affect the number of genes, metabolisms, and populations in a microbial community. In particular, for microbial communities, the model predicts that the diversity of taxa, their genes, and metabolisms should respond to temperature according to the PLECO model, and after scaling the data using the estimated parameters, all data should collapse into a single curve. To test these predictions, we use global hot springs microbial communities; geothermally heated environments that include aquatic and terrestrial habitats with large temperature gradients. We analyzed a global database (five continents) of 19 hot springs metagenomes covering a wide gradient of temperature (32-90°C). We found that the alpha diversity of taxa, genes, and their metabolisms decreases with temperature, in agreement with the predictions of the PLECO model. Further, after non-dimensionalization of the model, we derive a single nondimensional curve for taxa and functions. Finally, using general linear models, we analyzed the effects of pH, latitude, and substrate (soil, water, or both), in addition to temperature, to explain the observed diversity pattern. We find that they explain a lower proportion of the variance, but pH can explain up to half of the variance in global diversity in these ecosystems, indicating the need to include pH in the theory. Our study supports the hypothesis that temperature regulates the structure of community genomes.