Surface chemical reactivity and metal adsorptive properties of natural cyanobacterial mats from an alkaline hydrothermal spring, Yellowstone National Park S.V. Lalonde a, ⁎ , L.A. Amskold a , L.A. Warren b , K.O. Konhauser a a Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E3 b School of Geography and Earth Sciences, 309 General Science Building, McMaster University, Hamilton, ON, Canada L8S 4K1 Received 11 November 2006; received in revised form 11 May 2007; accepted 16 May 2007 Editor: D. Rickard Abstract The propensity for microbes to adsorb dissolved metals onto their surfaces has been well documented, to the point where predictive surface complexation models can accurately account for these reactions under experimental conditions. However, critical surface chemical parameters, such as surface functional group concentrations and proton stability constants, have only been evaluated using laboratory cultures. Whether or not natural microbes are comparable in surface chemical reactivity to laboratory cultures, and whether they display variations across diverse populations, remains untested. To resolve this, we examined natural cyanobacterial mats of various morphologies (i.e., streamers, vertical spires, horizontally laminated structures), sampled from a single hydrothermal system in Yellowstone National Park, in terms of surface chemical parameters and acid-leachable metal contents. Potentiometric titration data of samples that were acid-washed to remove sorbed metals and reveal underlying organic surfaces indicated functional group concentrations of 0.98 ± 0.28 to 2.84 ± 0.41 mmol g - 1 (dry weight) summed over a pK a range of 4 to 10, which is comparable to previously reported experimental values. In contrast, samples that were not acid-washed, but merely rinsed in titration electrolyte adjusted to stream pH, had functional group concentrations ranging from 6.12 ± 1.39 to 19.23 ± 3.14 mmol g - 1 . They were also largely dominated by a single functional group of pK a ∼ 7 that may be explained by the presence of aqueous or solid phase metal carbonate species that are removed from the mats by acid-washing. Analysis of the acid-wash solutions indicate that different metals were concentrated to varying extents, and that metals with low metal-carbonate solubility products, such as Ba, Ca, Fe, Mg, Mn, Ni, Sr, and Zn, were preferentially concentrated by the mats, perhaps as the result of precipitation as, or complexation with, mat-hosted carbonate species. These results highlight the complexity of metal partitioning in natural microbial communities, where a variety of processes other than surface adsorption, such as metabolism, authigenic mineral precipitation, and the physical entrapment of detrital material, may contribute to metal sequestration. Crown Copyright © 2007 Published by Elsevier B.V. All rights reserved. Keywords: Surface chemistry; Metal adsorption; Cyanobacteria; Microbial mats 1. Introduction Microbes are found in nearly every aqueous environment on Earth, where their highly reactive sur- faces effectively adsorb metals to such an extent that Chemical Geology 243 (2007) 36 – 52 www.elsevier.com/locate/chemgeo ⁎ Corresponding author. Tel.: +1 780 492 6532; fax: +1 780 492 2030. E-mail address: stefan.lalonde@ualberta.ca (S.V. Lalonde). 0009-2541/$ - see front matter. Crown Copyright © 2007 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2007.05.016