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Published July 9, 2013 | Supplemental Material + Published
Journal Article Open

Manganese-oxidizing photosynthesis before the rise of cyanobacteria


The emergence of oxygen-producing (oxygenic) photosynthesis fundamentally transformed our planet; however, the processes that led to the evolution of biological water splitting have remained largely unknown. To illuminate this history, we examined the behavior of the ancient Mn cycle using newly obtained scientific drill cores through an early Paleoproterozoic succession (2.415 Ga) preserved in South Africa. These strata contain substantial Mn enrichments (up to ∼17 wt %) well before those associated with the rise of oxygen such as the ∼2.2 Ga Kalahari Mn deposit. Using microscale X-ray spectroscopic techniques coupled to optical and electron microscopy and carbon isotope ratios, we demonstrate that the Mn is hosted exclusively in carbonate mineral phases derived from reduction of Mn oxides during diagenesis of primary sediments. Additional observations of independent proxies for O_2—multiple S isotopes (measured by isotope-ratio mass spectrometry and secondary ion mass spectrometry) and redox-sensitive detrital grains—reveal that the original Mn-oxide phases were not produced by reactions with O_2, which points to a different high-potential oxidant. These results show that the oxidative branch of the Mn cycle predates the rise of oxygen, and provide strong support for the hypothesis that the water-oxidizing complex of photosystem II evolved from a former transitional photosystem capable of single-electron oxidation reactions of Mn.

Additional Information

© 2013 National Academy of Sciences. Freely available online through the PNAS open access option. Edited by Andrew H. Knoll, Harvard University, Cambridge, MA, and approved May 22, 2013 (received for review March 25, 2013. Published online before print June 24, 2013. We thank James Hemp for valuable manuscript feedback; Yunbin Guan and Chi Ma for assistance with SIMS and SEM data collection; Kristin Bergmann for discussions and analytical assistance; and George Rossman, Nic Beukes, Benjamin Kocar, John Eiler, Tim Raub, and John Abelson for helpful discussions and laboratory and field assistance. We thank four anonymous reviewers for valuable insights. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the US Department of Energy Office of Science by Stanford University. Support for this work was provided by the Agouron Institute, National Aeronautics and Space Administration Exobiology (W.W.F.), the David and Lucile Packard Foundation (W.W.F.), and the National Science Foundation Graduate Research Fellowship program (J.E.J.). Author contributions: J.E.J., J.L.K., and W.W.F. designed research; J.E.J., S.M.W., K.T., S.O., and W.W.F. performed research; S.M.W. contributed new reagents/analytic tools; J.E.J., S.M.W., K.T., S.O., and W.W.F. analyzed data; and J.E.J. and W.W.F. wrote the paper.

Attached Files

Published - PNAS-2013-Johnson-11238-43.pdf

Supplemental Material - pnas.201305530SI.pdf

Supplemental Material - st01.docx

Supplemental Material - st02.docx

Supplemental Material - st03.docx


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