Metal Resistance and Lithoautotrophy in the Extreme Thermoacidophile Metallosphaera sedula

Abstract

ABSTRACTArchaea such asMetallosphaera sedulaare 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 (CuFeS2). In this study, a genetic system was developed forM. sedulato investigate parameters that limit bioleaching of chalcopyrite. The functional role of theM. sedula copRTAoperon was demonstrated by cross-species complementation of a copper-sensitiveSulfolobus solfataricus copRmutant. Inactivation of the gene encoding theM. sedulacopper efflux protein,copA, using targeted recombination compromised metal resistance and eliminated chalcopyrite bioleaching. In contrast, a spontaneousM. sedulamutant (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 (BaCO3) 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.