Image: Journal of Aquatic Geochemistry: "Microbial Acid Sulfate Weathering of Basaltic Rocks: Implication for Enzymatic Reactions" Authors: Fatih Sekerci1 and Nurgul Balci12 1 Geomicrobiology-Biogeochemistry Laboratory, Department of Geological Engineering, Istanbul Technical University, Istanbul, Turkey 2 Department of Geology, University of Georgia, Athens, USA Abstract Two basaltic rocks were reacted in acid sulfate and non-acid sulfate solutions with an initial pH value of 2 in the presence and absence of A. ferrooxidans to determine if basalt dissolution can support the metabolically active growth of A. ferrooxidans. Similar elemental release rates (RSi, RCa, RMg) calculated for both biotic and abiotic experiments suggest rather a negligible microbial impact on the dissolution of basaltic rocks within the acid sulfate solution. Nevertheless, in contrast with the abiotic experiments, measurements of remarkably high concentration of Fe(III)aq in microbial experiments confirmed the bacterial metabolism. Moreover, detected cell division and increasing total cell numbers with the extent of the experiments provide further evidence for the growth of metabolically active A. ferrooxidans during the dissolution of the rocks. Formation of jarosite ((K, Na, H3O)Fe3(SO4)2(OH)6) only in the biotic experiments is attributed to the microbially catalyzed Fe(II)aq oxidation. Overall, our results showed that acidic solutions that reacted with basaltic rocks can sustain the growth of Fe(II)aq oxidizing bacteria. Furthermore, identification of jarosite only in the biotic experiments emphasizes the enzymatic Fe(II) oxidation as the key step for its formation during basalt weathering at acid conditions, highlighting its biosignature potential on Earth and Earth-like planets (e.g., Mars). DOI: https://doi.org/10.1007/s10498-022-09407-8 Fig 1: Petrographic photomicrographs of BS1 rock sample under plane polarized (a, c) and cross polarized light (b, d). px: clinopyroxene, plg: plagioclase, il: ilmenite Fig 2: Petrographic photomicrographs of BS2 rock sample under plane polarized (a, c) and cross polarized light (b, d). px: clinopyroxene, plg: plagioclase, il: ilmenite Fig 9: SEM photomicrographs of the abiotically reacted basaltic grains in acid sulfate solution. a) Surface of the pre-reacted BS1 grains. b-c) Surface of the post-reacted BS1-AB grains. d) A closer view of the red square in c. e) EDS spectra of a. f) EDS spectra of the post-reacted basalt grains in d Fig 10: SEM photomicrographs of the abiotically reacted basaltic grains in acid sulfate solution. a Surface of the pre-reacted BS2 grains. b-c Surface of the post-reacted BS2-B grains. d A closer view of the red square in c. e EDS spectra of a. f EDS spectra of the post-reacted basalt grains in d Fig 13: Comparison of previously reported Si release rates with the present study Read More: Read the full articel at Springer - Aquatic Geochistry (2022)
