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Oxygen isotope analysis of bacterial and fungal manganese oxidation
Author(s) -
Sutherland K. M.,
Wankel S. D.,
Hansel C. M.
Publication year - 2018
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/gbi.12288
Subject(s) - manganese , oxygen , chemistry , environmental chemistry , isotopes of oxygen , nuclear chemistry , organic chemistry
The ability of micro‐organisms to oxidize manganese (Mn) from Mn( II ) to Mn( III / IV ) oxides transcends boundaries of biological clade or domain. Many bacteria and fungi oxidize Mn( II ) to Mn( III / IV ) oxides directly through enzymatic activity or indirectly through the production of reactive oxygen species. Here, we determine the oxygen isotope fractionation factors associated with Mn( II ) oxidation via various biotic (bacteria and fungi) and abiotic Mn( II ) reaction pathways. As oxygen in Mn( III / IV ) oxides may be derived from precursor water and molecular oxygen, we use a twofold approach to determine the isotope fractionation with respect to each oxygen source. Using both 18 O‐labeled water and closed‐system Rayleigh distillation approaches, we constrain the kinetic isotope fractionation factors associated with O atom incorporation during Mn( II ) oxidation to −17.3‰ to −25.9‰ for O 2 and −1.9‰ to +1.8‰ for water. Results demonstrate that stable oxygen isotopes of Mn( III / IV ) oxides have potential to distinguish between two main classes of biotic Mn( II ) oxidation: direct enzymatic oxidation in which O 2 is the oxidant and indirect enzymatic oxidation in which superoxide is the oxidant. The fraction of Mn( III / IV ) oxide‐associated oxygen derived from water varies significantly (38%–62%) among these bio‐oxides with only weak relationship to Mn oxidation state, suggesting Mn( III ) disproportionation may account for differences in the fraction of mineral‐bound oxygen from water and O 2 . Additionally, direct incorporation of molecular O 2 suggests that Mn( III / IV ) oxides contain a yet untapped proxy ofδ 18 O O 2of environmental O 2 , a parameter reflecting the integrated influence of global respiration, photorespiration, and several other biogeochemical reactions of global significance.