Identification of Components of Electron Transport Chains in the Extremely Thermoacidophilic Crenarchaeon Metallosphaera sedula through Iron and Sulfur Compound Oxidation Transcriptomes

Abstract

The crenarchaeal order Sulfolobales collectively contain at least five major terminal oxidase complexes. Based on genome sequence information, all five complexes are found only in Metallosphaera sedula and Sulfolobus tokodaii, the two sequenced Sulfolobales capable of iron oxidization. While specific respiratory complexes in certain Sulfolobales have been characterized previously as proton pumps for maintaining intracellular pH and generating proton motive force, their contribution to sulfur and iron biooxidation has not been considered. For M. sedula growing in the presence of ferrous iron and reduced inorganic sulfur compounds (RISCs), global transcriptional analysis was used to track the response of specific genes associated with these complexes, as well as other known and putative respiratory electron transport chain elements. Open reading frames from all five terminal oxidase or bc 1 -like complexes were stimulated on one or more conditions tested. Components of the fox (Msed0467 to Msed0489) and soxNL-cbsABA (Msed0500 to Msed0505) terminal/quinol oxidase clusters were triggered by ferrous iron, while the soxABCDD terminal oxidase cluster (Msed0285 to Msed0291) were induced by tetrathionate and S 0 . Chemolithotrophic electron transport elements, including a putative tetrathionate hydrolase (Msed0804), a novel polysulfide/sulfur/dimethyl sulfoxide reductase-like complex (Msed0812 to Msed0818), and a novel heterodisulfide reductase-like complex (Msed1542 to Msed1550), were also stimulated by RISCs. Furthermore, several hypothetical proteins were found to have strong responses to ferrous iron or RISCs, suggesting additional candidates in iron or sulfur oxidation-related pathways. From this analysis, a comprehensive model for electron transport in M. sedula could be proposed as the basis for examining specific details of iron and sulfur oxidation in this bioleaching archaeon.Certain extremely thermoacidophilic archaea are promising candidates for biomining operations targeting the recovery of base and precious metals (44). These microorganisms grow at elevated temperatures where abiotic ferrous oxidation rates are accelerated and where passivation of mineral surfaces from reduced inorganic sulfur compounds (RISCs) is minimal (44). To tap into the biotechnological potential of these microorganisms, their physiological characteristics that relate to metal mobilization need to be better understood, especially mechanisms underlying biooxidation of iron (Fe 2ϩ ) and RISCs. Biooxidation implicates membrane-associated protein complexes that mediate electron transport, which seemingly determines the capability and capacity of extreme thermoacidophiles for metal and sulfur mobilization. However, the complexes required for bioleaching have not been established. Models that address the specific and collective function of electron transport complexes in the Sulfolobales are needed to provide a physiological framework for exploring the intricacies of biological metal and sulfur oxidation.Current knowledge of respiratory el...

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

“…E xtremely thermoacidophilic archaea from the genera Sulfolobus, Acidianus, and Metallosphaera can inhabit natural and anthropogenic environments laden with metals (1) and, as a consequence, require strategies to avert the deleterious impact of these metals on cellular function (2). For some species within the Sulfolobales, metal oxidation mediated by membrane-bound, oxidase clusters provides a cellular bioenergetic benefit (3)(4)(5). However, at the same time, utilization of this energy source contributes to the toxicity of the biotope by mobilizing metal cations that can subsequently inhibit biological function (6,7).…”

Impact of Molecular Hydrogen on Chalcopyrite Bioleaching by the Extremely Thermoacidophilic Archaeon Metallosphaera sedula

“…The resulting total soluble iron levels were determined, such that the total iron release reported for CO 2 -enhanced cultures includes contributions from the precipitate that accumulated on culture vessel walls. It should be noted that 6 days after inoculation, total iron levels in solution were the same for air headspace cultures as for CO 2 -enhanced headspace cultures (data not shown); no iron contribution from wall precipitates was included for air-only cultures. Specific bioleaching rates were calculated by dividing the average cell density (note that cells were counted in a two-dimensional space; therefore, cells attached to the bottom of particles would have been missed for both culture conditions) during the 6-day postinoculation period by the total amount of iron released from the chalcopyrite during the same time.…”

“…Metallosphaera sedula, an extremely thermoacidophilic, metal-mobilizing crenarchaeon growing optimally at 70 to 75°C and pH 2 (3), has been examined in this regard (7,11). Key to bioleaching capacity in this microorganism is the dissimilatory oxidation of iron and sulfur, mediated by membrane-associated electron transport chains that are anchored by terminal oxidases (2,3,12). For M. sedula, another factor that needs to be considered is the impact of inorganic energy sources, other than metal sulfides, on bioleaching.…”

“…Cultures growing exponentially were harvested 1 day postinoculation and compared to CuFeS 2 -grown cultures that were harvested 3 or 9 days postinoculation. Harvesting was done as previously described (2,3). Methods used for microarray construction, RNA preparation, slide scanning, and data analysis were also as described previously, with the exception that Trizol (Invitrogen) was used as the RNA extraction reagent and a Packard BioChip Scanarray 4000 scanner was used for slide scanning.…”

Complete Genome Sequence of Metallosphaera cuprina, a Metal Sulfide-Oxidizing Archaeon from a Hot Spring

“…Oxidation of RISCs by the heterodisulfide reductase complex, sulfide:quinone oxidoreductase, thiosulfate:quinone oxidoreductase, tetrathionate hydrolase, and sulfite:acceptor oxidoreductase in M. cuprina was proposed. The terminal oxidase complexes of M. cuprina that channel electrons from RISC oxidation to oxygen were similar to those of "Metallosphaera yellowstonensis" (7) and M. sedula (1).…”