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Front. Microbiol. | doi: 10.3389/fmicb.2019.00271

Insights into the mineralogy and surface chemistry of extracellular biogenic S(0) globules produced by Chlorobaculum tepidum

 Cassandra L. Marnocha1, 2*, Chandran R. Sabanayagam3,  Shannon Modla3, Deborah H. Powell3,  Pauline A. Henri2, Andrew Steele4,  Thomas E. Hanson2, 3,  Samuel M. Webb5 and  Clara S. Chan2, 3*
  • 1Niagara University, United States
  • 2University of Delaware, United States
  • 3Delaware Biotechnology Institute, United States
  • 4Carnegie Institution for Science (CIS), United States
  • 5SLAC National Accelerator Laboratory, Stanford Synchrotron Radiation Lightsource, United States

Elemental sulfur (S0) is produced and degraded by a diverse group of microorganisms. For Chlorobaculum tepidum, an anoxygenic phototroph, sulfide is oxidized to produce extracellular S0 globules, which can be further oxidized to sulfate. While some sulfur-oxidizing bacteria (e.g. Al. vinosum) are also capable of growth on commercial S0 as an electron donor, Cba. tepidum is not. Even colloidal sulfur sols, which appear indistinguishable from biogenic globules, do not support the growth of Cba. tepidum. Here, we investigate the properties that make biogenic S0 globules special and distinct from abiotic forms of S0. We found that S0 globules produced by Cba. tepidum and abiotic S0 sols are quite similar in terms of mineralogy and material properties, but the two are distinguished primarily by the properties of their surfaces. Cba. tepidum’s globules are enveloped by a layer of organics (protein and polysaccharides), which results in a surface that is fundamentally different from that of abiotic S0 sols. The organic coating on the globules appears to slow the aging and crystallization of amorphous sulfur, perhaps providing an extended window of time for microbes in the environment to access the more labile forms of sulfur as needed. Overall, our results suggest that the surface of biogenic S0 globules may be key to cell-sulfur interactions and the reactivity of biogenic S0 in the environment.

Keywords: Elemental sulfur, Biomineralization, sulfur cycling, Green sulfur bacteria, microbe-mineral interactions

Received: 05 Oct 2018; Accepted: 01 Feb 2019.

Edited by:

Alexander Loy, University of Vienna, Austria

Reviewed by:

Alexey Kamyshny, Ben-Gurion University of the Negev, Israel
Trinity L. Hamilton, University of Minnesota Twin Cities, United States  

Copyright: © 2019 Marnocha, Sabanayagam, Modla, Powell, Henri, Steele, Hanson, Webb and Chan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Dr. Cassandra L. Marnocha, Niagara University, Lewiston, United States, cmarnocha@niagara.edu
Dr. Clara S. Chan, Delaware Biotechnology Institute, Newark, 19711, California, United States, cschan@udel.edu