43018 2017 eng 9691 9699 17 51 article ACS Publications USA American Chemical Society 1 -- -- -- The model rock-inhabiting microcolonial fungus Knufia petricola fractionates stable Mg isotopes in a time and pH-dependent manner. During growth, the increase of 26Mg/24Mg in the fungal cells relative to the growth media amounted to 0.65 ± 0.14‰at pH 6 and 1.11 ± 0.35‰at pH 3. We suggest a constant equilibrium fractionation factor during incorporation of Mg into ribosomes and ATP as a cause of enrichment of 26Mg in the cells. We suggest too that the proton gradient across the cell wall and cytoplasmic Membrane controls Mg2+ transport into the fungal cell. As the strength of this gradient is a function of extracellular solution pH, the pHdependence on Mg isotope fractionation is thus due to differences in fungal cell mass fluxes. Through a mass balance model we show that Mg uptake into the fungal cell is not associated with a unique Mg isotope fractionation factor. This Mg isotope fractionation dependence on pH might also be observed in any organism with cells that follow similar Mg uptake and metabolic pathways and serves to reveal Mg cycling in ecosystems. Environmental Science and Technology 10.1021/acs.est.7b01798 0013-936X 1520-5851 21.11.2017 Pokharel Rasesh Ruben Gerrits Jan A. Schuessler Geerke H. Floor Anna Gorbushina Friedhelm von Blanckenburg eng uncontrolled Isotope fractionation eng uncontrolled Fungus eng uncontrolled Magnesium Sanitär- und Kommunaltechnik; Umwelttechnik Verlagsliteratur Datei im Netzwerk der BAM verfügbar ("Closed Access")