Respiratory gene clusters of Metallosphaera sedula – differential expression and transcriptional organization

Abstract

Metallosphaera sedula is a thermoacidophilic Crenarchaeon which is capable of leaching metals from sulfidic ores. The authors have investigated the presence and expression of genes encoding respiratory complexes in this organism when grown heterotrophically or chemolithotrophically on either sulfur or pyrite. The presence of three gene clusters, encoding two terminal oxidase complexes, the quinol oxidase SoxABCD and the SoxM oxidase supercomplex, and a gene cluster encoding a high-potential cytochrome b and components of a bc 1 complex analogue (cbsBA-soxL2N gene cluster) was established. Expression studies showed that the soxM gene was expressed to high levels during heterotrophic growth of M. sedula on yeast extract, while the soxABCD mRNA was most abundant in cells grown on sulfur. Reduced-minus-oxidized difference spectra of cell membranes showed cytochrome-related peaks that correspond to published spectra of Sulfolobus-type terminal oxidase complexes. In pyrite-grown cells, expression levels of the two monitored oxidase gene clusters were reduced by a factor of 10-12 relative to maximal expression levels, although spectra of membranes clearly contained oxidase-associated haems, suggesting the presence of additional gene clusters encoding terminal oxidases in M. sedula. Pyrite-and sulfur-grown cells contained high levels of the cbsA transcript, which encodes a membrane-bound cytochrome b with a possible role in iron oxidation or chemolithotrophy. The cbsA gene is not co-transcribed with the soxL2N genes, and therefore does not appear to be an integral part of this bc 1 complex analogue. The data show for the first time the differential expression of the Sulfolobus-type terminal oxidase gene clusters in a Crenarchaeon in response to changing growth modes.

The Genome Sequence of the Metal-Mobilizing, Extremely Thermoacidophilic Archaeon Metallosphaera sedula Provides Insights into Bioleaching-Associated Metabolism

“…Because locus 1 soxB (Msed0290) was reported to be upregulated on S 0 , compared to FeS 2 or YE (36), and DoxBCE expression and copurification with TQO subunits (DoxDA) were noted under S 0 -oxidizing conditions in A. ambivalens (45,54), it seems likely that the locus 1 and 5 respiratory clusters in M. sedula would also be stimulated during growth on RISCs. Locus 2 soxM (Msed0324) was reported as being up-regulated on YE, compared to FeS 2 or S 0 (36).…”

“…Despite the annotation, tetrathionate hydrolases (TetH) expressed on S 0 , FeS 2 , and S 2 O 3 2Ϫ substrates have been noted in A. ferrooxidans and Acidithiobacillus caldus (8,35,61). Certain terminal oxidase components have been expressed in extremely thermoacidophilic archaea grown on specific RISCs (36,54). Although not directly linked to electron transport, sulfur oxygenase reductases (Sor) are believed to be important for breakdown of intracellular RISCs, particularly S 0 or polysulfides (11,37,69 Although M. sedula presumably grows mixotrophically, autotrophy is critical in biomining environments, where relatively small amounts of organic carbon are available.…”

“…Components of electron transport chains involved in Fe and RISC oxidation are differentially expressed as a function of substrate in both meso-and thermoacidophilic bioleachers (5,36,55). Bacterial Fe oxidation studies focused on mesophilic A. ferrooxidans have shown that electrons from Fe(II) can be transported along either a "downhill" or an "uphill" electron pathway, towards a lower (O 2 /H 2 O)-or higher [NAD(P) ϩ / NAD(P)H]-potential redox couple, respectively (28).…”

Characterization of an ntrX Mutant of Neisseria gonorrhoeae Reveals a Response Regulator That Controls Expression of Respiratory Enzymes in Oxidase-Positive Proteobacteria

“…The identity of the strain, designated the Rc-ntrX mutant, was confirmed by Southern blotting using digoxigenin (DIG)-dUTP (Roche Biochemicals, NSW, Australia)-labeled DNA probes as described previously (32). Selection and propagation of Rc-ntrX mutants were carried out aerobically on antibiotic-supplemented TYS medium (26).…”

Metal Resistance and Lithoautotrophy in the Extreme Thermoacidophile Metallosphaera sedula

“…Recovery rates of copper bioleached from chalcopyrite ranged from 10 to 25% (16), and the recently discovered Metallosphaera cuprina was shown to mobilize 10.6% of total copper when grown on chalcopyrite (23). Elucidation of the genome sequence of several biomining organisms (5,24,45) along with transcriptomic analyses (4,20) supports investigations into strategies that underlie lithoautotrophic metabolism.…”