Metal Resistance and Lithoautotrophy in the Extreme Thermoacidophile Metallosphaera sedula

Abstract

Archaea such as Metallosphaera sedula are thermophilic lithoautotrophs that occupy unusually acidic and metal-rich environments. These traits are thought to underlie their industrial importance for bioleaching of base and precious metals. In this study, a genetic approach was taken to investigate the specific relationship between metal resistance and lithoautotrophy during biotransformation of the primary copper ore, chalcopyrite (CuFeS 2 ). In this study, a genetic system was developed for M. sedula to investigate parameters that limit bioleaching of chalcopyrite. The functional role of the M. sedula copRTA operon was demonstrated by cross-species complementation of a copper-sensitive Sulfolobus solfataricus copR mutant. Inactivation of the gene encoding the M. sedula copper efflux protein, copA, using targeted recombination compromised metal resistance and eliminated chalcopyrite bioleaching. In contrast, a spontaneous M. sedula mutant (CuR1) with elevated metal resistance transformed chalcopyrite at an accelerated rate without affecting chemoheterotrophic growth. Proteomic analysis of CuR1 identified pleiotropic changes, including altered abundance of transport proteins having AAA-ATPase motifs. Addition of the insoluble carbonate mineral witherite (BaCO 3 ) further stimulated chalcopyrite lithotrophy, indicating that carbon was a limiting factor. Since both mineral types were actively colonized, enhanced metal leaching may arise from the cooperative exchange of energy and carbon between surface-adhered populations. Genetic approaches provide a new means of improving the efficiency of metal bioleaching by enhancing the mechanistic understanding of thermophilic lithoautotrophy.N early 80% of current global copper reserves are comprised of low-quality metal ores (10,25,44). Consequently, the need for cost-efficient extraction methods has promoted interest in the use of microbe-based processing. Bioleaching is an established approach for the extraction of base and precious metals from sulfidic ores (30,34,35,43). Bioleaching using thermophilic microbes is of particular importance for certain metals. In the case of copper, elevated temperatures produced naturally in heaps overcome recalcitrant extraction due to surface passivation while chemical reaction rates are accelerated (29,30). A critical disadvantage of bioleaching is the amount of time required for metal solubilization, often spanning years (22,38). Therefore, improved metal recovery must include factors that accelerate this process, particularly those inspired by biotechnologic approaches (48).Thermoacidophilic archaea include taxa that are lithoautotrophic and unusually metal resistant (3,19). These organisms are native to pyritic or sulfur-rich geothermal habitats and are used to recover base and precious metals from low-quality sulfidic minerals through bioleaching processes (31). In the bioleaching process, both direct and indirect leaching mechanisms have been proposed that convert metals to soluble forms (33, 40). Metal release may occur via metab...

Transcriptomes of the Extremely Thermoacidophilic Archaeon Metallosphaera sedula Exposed to Metal “Shock” Reveal Generic and Specific Metal Responses

“…Resistance to copper in extreme thermoacidophiles is mediated at least by mechanisms involving active transport and metal sequestration (7,(10)(11)(12)(13)(14)(15) Citation Wheaton GH, Mukherjee A, Kelly RM. 2016.…”

Experimental Microbial Evolution of Extremophiles

“…This means that ALE studies require longer time periods to achieve equivalent number of generations. For example, this is especially true for extremophiles cultivated under lithoautotrophic conditions where energy limitation constrains replication rate (McCarthy et al 2014;Maezato et al 2012). …”

“…Recombinant expression of extremophile proteins in non-extremophile hosts such as E. coli often face a similar problem: outside of the extreme conditions of their native environments halophilic proteins have a tendency to misfold and aggregate (Allers 2010). For these reasons, examining the performance of evolved extremophilic macromolecules within the native extremophile host becomes critical and depends on the availability of genetic systems (Maezato et al 2012). …”

“…The sample is then mixed and flash frozen using an ethanol-dry ice bath. Storage at −80 °C provides a long term method to preserve culturability (Maezato et al 2012).…”

BioRock: new experiments and hardware to investigate microbe–mineral interactions in space

“…These solutions will be examined by inductively coupled BioRock: investigating microbe-mineral interactions in space 9 plasma mass and optical emission spectrometry (ICP-MS/ OES), (Maezato et al 2012). This result will aid the determination of if and how microgravity alters the ability to extract minerals from the rock for the investigated organisms.…”