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Published September 2013 | public
Journal Article

Filamentous sulfur bacteria preserved in modern and ancient phosphatic sediments: implications for the role of oxygen and bacteria in phosphogenesis

Abstract

Marine phosphate-rich sedimentary deposits (phosphorites) are important geological reservoirs for the biologically essential nutrient phosphorous. Phosphorites first appear in abundance approximately 600 million years ago, but their proliferation at that time is poorly understood. Recent marine phosphorites spatially correlate with the habitats of vacuolated sulfide-oxidizing bacteria that store polyphosphates under oxic conditions to be utilized under sulfidic conditions. Hydrolysis of the stored polyphosphate results in the rapid precipitation of the phosphate-rich mineral apatite—providing a mechanism to explain the association between modern phosphorites and these bacteria. Whether sulfur bacteria were important to the formation of ancient phosphorites has been unresolved. Here, we present the remains of modern sulfide-oxidizing bacteria that are partially encrusted in apatite, providing evidence that bacterially mediated phosphogenesis can rapidly permineralize sulfide-oxidizing bacteria and perhaps other types of organic remains. We also describe filamentous microfossils that resemble modern sulfide-oxidizing bacteria from two major phosphogenic episodes in the geologic record. These microfossils contain sulfur-rich inclusions that may represent relict sulfur globules, a diagnostic feature of modern sulfide-oxidizing bacteria. These findings suggest that sulfur bacteria, which are known to mediate the precipitation of apatite in modern sediments, were also present in certain phosphogenic settings for at least the last 600 million years. If polyphosphate-utilizing sulfide-oxidizing bacteria also played a role in the formation of ancient phosphorites, their requirements for oxygen, or oxygen-requiring metabolites such as nitrate, might explain the temporal correlation between the first appearance of globally distributed marine phosphorites and increasing oxygenation of Neoproterozoic oceans.

Additional Information

© 2013 John Wiley & Sons Ltd. Received 18 January 2013; accepted 24 May 2013. Article first published online: 20 Jun. 2013. We thank Nick Seaton, Ellery Frahm, Anette von der Handt, Will Berelson, Chi Ma, and Bing Luo for assistance with the instrument analysis and sample preparation. We thank Greg Rouse for providing the photography used in Fig. 1B. We also thank Lisa Levin, Tony Rathburn and the participants and crew of cruise AT 15-44 (supported by the National Science Foundation OCE-0826254) for assisting with the collection of the samples from Costa Rica. We also thank three anonymous reviewers whose comments improved the manuscript. Portions of this work were supported by an Agouron Geobiology Postdoctoral Fellowship and National Science Foundation grant EAR-1057119 to JVB, and by the National Natural Science Foundation of China (41172035) and China Geology Survey (1212011120140). Additional funding was provided by an AAPG Kenneth H. Crandall Memorial Grant-in-Aid to SEG. Parts of this work were carried out in the Characterization Facility at the University of Minnesota, which receives partial support from NSF through the MRSEC program.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023