Biomineralization by Extremely Halophilic and Metal-Tolerant Community Members from a Sulfate-Dominated Metal-Rich Environment.

Marie Harpke,Clara Gansert,Erika Kothe,Falko Langenhorst,Flávio Silva Costa,Sebastian Pietschmann

doi:10.3390/microorganisms10010079

Marie Harpke, Clara Gansert + Show 4 more

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https://doi.org/10.3390/microorganisms10010079

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Abstract

The adaptation to adverse environmental conditions can lead to adapted microbial communities that may be screened for mechanisms involved in halophily and, in this case, metal tolerance. At a former uranium mining and milling site in Seelingstädt, Germany, microbial communities from surface waters and sediment soils were screened for isolates surviving high salt and metal concentrations. The high salt contents consisted mainly of chloride and sulfate, both in soil and riverbed sediment samples, accompanied by high metal loads with presence of cesium and strontium. The community structure was dominated by Chloroflexi, Proteobacteria and Acidobacteriota, while only at the highest contaminations did Firmicutes and Desulfobacterota reach appreciable percentages in the DNA-based community analysis. The extreme conditions providing high stress were mirrored by low numbers of cultivable strains. Thirty-four extremely halotolerant bacteria (23 Bacillus sp. and another 4 Bacillales, 5 Actinobacteria, and 1 Gamma-Proteobacterium) surviving 25 to 100 mM SrCl2, CsCl, and Cs2SO4 were further analyzed. Mineral formation of strontium- or cesium-struvite could be observed, reducing bioavailability and thereby constituting the dominant metal and salt resistance strategy in this environment.

Highlights

Environments with high salt concentrations such as brines, salty soils, or sediments drive adaptation of the microbial community present at such sites [1,2,3,4]
Specific contaminants include NaCl, but due to mining operations of sulfidic ores, high sulfate concentrations may lead to halophilic communities establishing on such sites [5,6,7]
The co-occurrence of metal ions poses another stress on the microbial community, which results in co-tolerance [10,11]

Summary

Introduction

Environments with high salt concentrations such as brines, salty soils, or sediments drive adaptation of the microbial community present at such sites [1,2,3,4]. Former mining sites are associated with circum-neutral or even acidic pH, the latter promoting metal leaching. The co-occurrence of metal ions poses another stress on the microbial community, which results in co-tolerance [10,11]. An example of such a site where acid mine drainage with high metal and sulfate loads at circum-neutral pH is the former uranium mining and milling site near Seelingstädt, Germany, where remediation activities started in 1990 including dry in situ stabilization of the tailings, re-vegetation, and the treatment of seepage waters [12,13]. In the 1960s, one tailings dam failed, releasing tailings material that was subsequently removed [15]

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