Papers in the Biological Sciences


Date of this Version



Applied and Environmental Microbiology, Feb. 2008, p. 682–692, Vol. 74, No. 3


Copyright © 2008, American Society for Microbiology. All Rights Reserved.


Despite their taxonomic description, not all members of the order Sulfolobales are capable of oxidizing

reduced sulfur species, which, in addition to iron oxidation, is a desirable trait of biomining microorganisms.

However, the complete genome sequence of the extremely thermoacidophilic archaeon Metallosphaera sedula

DSM 5348 (2.2 Mb, _2,300 open reading frames [ORFs]) provides insights into biologically catalyzed metal

sulfide oxidation. Comparative genomics was used to identify pathways and proteins involved (directly or

indirectly) with bioleaching. As expected, the M. sedula genome contains genes related to autotrophic carbon

fixation, metal tolerance, and adhesion. Also, terminal oxidase cluster organization indicates the presence of

hybrid quinol-cytochrome oxidase complexes. Comparisons with the mesophilic biomining bacterium Acidithiobacillus

ferrooxidans ATCC 23270 indicate that the M. sedula genome encodes at least one putative rusticyanin,

involved in iron oxidation, and a putative tetrathionate hydrolase, implicated in sulfur oxidation. The

fox gene cluster, involved in iron oxidation in the thermoacidophilic archaeon Sulfolobus metallicus, was also

identified. These iron- and sulfur-oxidizing components are missing from genomes of nonleaching members of

the Sulfolobales, such as Sulfolobus solfataricus P2 and Sulfolobus acidocaldarius DSM 639. Whole-genome

transcriptional response analysis showed that 88 ORFs were up-regulated twofold or more in M. sedula upon

addition of ferrous sulfate to yeast extract-based medium; these included genes for components of terminal

oxidase clusters predicted to be involved with iron oxidation, as well as genes predicted to be involved with

sulfur metabolism. Many hypothetical proteins were also differentially transcribed, indicating that aspects of

the iron and sulfur metabolism of M. sedula remain to be identified and characterized.

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