An ecophysiological explanation for manganese enrichment in rock varnish

Usha F. Lingappa*, Chris M. Yeager, Ajay Sharma, Nina L. Lanza, Demosthenes P. Morales, Gary Xie, Ashley D. Atencio, Grayson L. Chadwick, Danielle R. Monteverde, John S. Magyar, Samuel M. Webb, Joan Selverstone Valentine*, Brian M. Hoffman, Woodward W. Fischer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Desert varnish is a dark rock coating that forms in arid environments worldwide. It is highly and selectively enriched in manganese, the mechanism for which has been a long-standing geological mystery. We collected varnish samples from diverse sites across the western United States, examined them in petrographic thin section using microscale chemical imaging techniques, and investigated the associated microbial communities using 16S amplicon and shotgun metagenomic DNA sequencing. Our analyses described a material governed by sunlight, water, and manganese redox cycling that hosts an unusually aerobic microbial ecosystem characterized by a remarkable abundance of photosynthetic Cyanobacteria in the genus Chroococcidiopsis as the major autotrophic constituent. We then showed that diverse Cyanobacteria, including the relevant Chroococcidiopsis taxon, accumulate extraordinary amounts of intracellular manganese—over two orders of magnitude higher manganese content than other cells. The speciation of this manganese determined by advanced paramagnetic resonance techniques suggested that the Cyanobacteria use it as a catalytic antioxidant—a valuable adaptation for coping with the substantial oxidative stress present in this environment. Taken together, these results indicated that the manganese enrichment in varnish is related to its specific uptake and use by likely founding members of varnish microbial communities.

Original languageEnglish (US)
Article numbere2025188118
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number25
StatePublished - Jun 22 2021


  • Rock varnish | desert varnish | Cyanobacteria manganese oxidative stress

ASJC Scopus subject areas

  • General


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