Seasonal Changes In Mineralogy, Geochemistry and Microbial Community of Bacteriogenic Iron Oxides (BIOS) Deposited in a Circumneutral Wetland

Abstract

Changes in the mineralogy, microbial community structure and aquatic geochemistry of bacteriogenic iron oxides (BIOS) deposited at a circumneutral groundwater seep were recorded seasonally. X-ray diffraction and X-ray absorption spectroscopy demonstrated that 2-line ferrihydrite dominated the iron-bearing mineralogy of the BIOS (>60%). Minor proportions of the more crystalline lepidocrocite were also detected in BIOS collected throughout the year (<30%), but goethite (<15%) was only identified in sediments collected during the spring, summer and fall months. Subsurface porewater profiles generally showed an increase in dissolved equilibrium concentrations of Fe(II), indicative of microbial Fe(III) reduction, and the depth at which appreciable levels of dissolved Fe(II) (and to a lesser extent manganese) arose, and sulfate concentrations declined, become shallower as the seasons progressed from spring to fall. Clone libraries constructed from 16S rRNA gene sequence analysis of surficial BIOS showed the presence of sequences closely affiliated to known Fe(II)-oxidizing and Fe(III)-reducing prokaryotes, pointing towards a tightly coupled microbial iron cycle. Clones that showed closest identity to Fe(II)-oxidizing bacteria in culture, including Gallionella spp. and Sideroxydans spp., made up a significant portion of the clone library, but their relative proportion declined through the winter (73%), spring (26%) and summer (9%). The dominance of the putative microaerophilic Fe(II)-oxidizing chemolithoautotrophs in the winter clone library may be partly due to the lower temperature and dissolved organic carbon concentrations observed during this season, conditions that could have limited mixotrophic or organotrophic growth by mesophilic bacteria. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file.

Keywords:

• Bacteriogenic iron oxides
• circumneutral iron oxidation
• iron reduction
• seasonal
• microbial diversity

Acknowledgments

Current affiliation for Robert Renaud: Trow Associates Inc., 154 Colonnade Rd., Ottawa, Ontario, K2E 7J5, Canada.Funding for this research was provided by a Natural Sciences and Engineering Research Council of Canada (NSERC) Strategic Project grant awarded to FGF (PI), DF and IDC. SL was supported by scholarships from NSERC, the Ontario Graduate Scholarship program, and the University of Ottawa. Synchrotron beam time was provided by SPring-8/JASRI awards (2008A1261, 2008B1528) to YT. Molecular ecology work was supported by a Natural Environment Research Council (UK) grant (NE/D005361/1) to JRL. We are especially grateful to Doug and Shelagh Ogilvie for their generous hospitality during fieldwork.