RESUMO
The genetic organization of the aioBA operon, encoding the arsenite oxidase of the moderately acidophilic and facultative chemoautotrophic bacterium Thiomonas arsenitoxydans, is different from that of the aioBA operon in the other arsenite oxidizers, in that it encodes AioF, a metalloprotein belonging to the ArsR/SmtB family. AioF is stabilized by arsenite, arsenate, or antimonite but not molybdate. Arsenic is tightly attached to AioF, likely by cysteine residues. When loaded with arsenite or arsenate, AioF is able to bind specifically to the regulatory region of the aio operon at two distinct positions. In Thiomonas arsenitoxydans, the promoters of aioX and aioB are convergent, suggesting that transcriptional interference occurs. These results indicate that the regulation of the aioBA operon is more complex in Thiomonas arsenitoxydans than in the other aioBA containing arsenite oxidizers and that the arsenic binding protein AioF is involved in this regulation. On the basis of these data, a model to explain the tight control of aioBA expression by arsenic in Thiomonas arsenitoxydans is proposed.
Assuntos
Arsênio/farmacologia , Betaproteobacteria/genética , Betaproteobacteria/metabolismo , Óperon , Oxirredutases/genética , Sequência de Aminoácidos , Antimônio/farmacologia , Arseniatos/farmacologia , Arsênio/química , Arsenitos/farmacologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Betaproteobacteria/efeitos dos fármacos , Sítios de Ligação , Cisteína/química , Regulação Bacteriana da Expressão Gênica/efeitos dos fármacos , Dados de Sequência Molecular , Molibdênio/farmacologia , Oxirredutases/metabolismo , Regiões Promotoras Genéticas , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismoRESUMO
Thiomonas arsenitoxydans is an acidophilic and facultatively autotrophic bacterium that can grow by oxidizing arsenite to arsenate. A comparative genomic analysis showed that the T. arsenitoxydans aioBA cluster encoding the two subunits of arsenite oxidase is distinct from the other clusters, with two specific genes encoding a cytochrome c and a metalloregulator belonging to the ArsR/SmtB family. These genes are cotranscribed with aioBA, suggesting that these cytochromes c are involved in arsenite oxidation and that this operon is controlled by the metalloregulator. The growth of T. arsenitoxydans in the presence of thiosulfate and arsenite, or arsenate, is biphasic. Real-time PCR experiments showed that the operon is transcribed during the second growth phase in the presence of arsenite or arsenate, whereas antimonite had no effect. These results suggest that the expression of the aioBA operon of T. arsenitoxydans is regulated by the electron donor present in the medium, i.e., is induced in the presence of arsenic but is repressed by more energetic substrates. Our data indicate that the genetic organization and regulation of the aioBA operon of T. arsenitoxydans differ from those of the other arsenite oxidizers.
Assuntos
Proteínas de Bactérias/genética , Betaproteobacteria/genética , Óperon , Oxirredutases/genética , Antimônio/metabolismo , Arseniatos/metabolismo , Arsênio/metabolismo , Arsenitos/metabolismo , Proteínas de Bactérias/metabolismo , Sequência de Bases , Betaproteobacteria/enzimologia , Betaproteobacteria/metabolismo , Genes Bacterianos , Dados de Sequência Molecular , Oxirredutases/metabolismoRESUMO
Bacteria of the Thiomonas genus are ubiquitous in extreme environments, such as arsenic-rich acid mine drainage (AMD). The genome of one of these strains, Thiomonas sp. 3As, was sequenced, annotated, and examined, revealing specific adaptations allowing this bacterium to survive and grow in its highly toxic environment. In order to explore genomic diversity as well as genetic evolution in Thiomonas spp., a comparative genomic hybridization (CGH) approach was used on eight different strains of the Thiomonas genus, including five strains of the same species. Our results suggest that the Thiomonas genome has evolved through the gain or loss of genomic islands and that this evolution is influenced by the specific environmental conditions in which the strains live.
Assuntos
Betaproteobacteria/genética , Evolução Molecular , Genoma Bacteriano/genética , Adaptação Fisiológica/genética , Arsênio/metabolismo , Carbono/metabolismo , Hibridização Genômica Comparativa , Metabolismo Energético/genética , Meio Ambiente , Transferência Genética Horizontal/genética , Genes Bacterianos/genética , Genes Duplicados/genética , Variação Genética , Ilhas Genômicas/genética , Redes e Vias Metabólicas/genética , Plasmídeos/genética , Prófagos/genéticaRESUMO
A moderately acidophilic, facultative chemoautotrophic, As(III)-oxidizing Thiomonas sp. (strain 3As(T)) was previously shown, on the basis of comparative 16S rRNA gene sequences, to be closely related to both Tm. perometabolis DSM 18570(T) and Tm. intermedia DSM 18155(T). While it had shared many physiological traits with Tm. intermedia (T), a mean DNA-DNA hybridization value (DDHV) of 47.2% confirmed that strain 3As(T) was not a strain of Tm. intermedia, though the situation with regard to Tm. perometabolis (DDHV previously determined as 72%) was more ambiguous. A comparative physiological and chemotaxonomic study of strain 3As(T) and Tm. perometabolis (T) was therefore carried out, together with multilocus sequence analysis (MLSA) of all three bacteria. Differences in fatty acid profiles and utilization of organic substrates supported the view that strain 3As(T) and Tm. perometabolis are distinct species, while MLSA showed a closer relationship between strain 3As(T) and Tm. intermedia (T) than between strain 3As(T) and Tm. perometabolis (T). These apparent contradictory conclusions were explained by differences in genome of these three bacteria, which are known to be highly flexible in Thiomonas spp. A novel species designation Thiomonas arsenitoxydans is proposed for strain 3As(T) (DSM 22701(T), CIP 110005(T)), which is nominated as the type strain of this species.
Assuntos
Arsênio/metabolismo , Betaproteobacteria/classificação , Betaproteobacteria/metabolismo , Betaproteobacteria/genética , Betaproteobacteria/crescimento & desenvolvimento , Crescimento Quimioautotrófico , DNA Bacteriano/genética , Ácidos Graxos/análise , Dados de Sequência Molecular , Tipagem de Sequências Multilocus , Filogenia , RNA Ribossômico 16S/genética , Enxofre/metabolismoRESUMO
Arsenic is a notorious poison classified as a carcinogen, a teratogen and a clastogen that ranks number one on the Environmental Protection Agency's priority list of drinking water contaminants. It is ubiquitous and relatively abundant in the Earth's crust. Its mobilization in waters by weathering, volcanic, anthropogenic or biological activities represents a major hazard to public health, exemplified in India and Bangladesh where 50 million people are acutely at risk. Since basically the origin of life, microorganisms have been exposed to this toxic compound and have evolved a variety of resistance mechanisms, such as extracellular precipitation, chelation, intracellular sequestration, active extrusion from the cell or biochemical transformation (redox or methylation). Arsenic efflux systems are widespread and are found in nearly all organisms. Some microorganisms are also able to utilize this metalloid as a metabolic energy source through either arsenite oxidation or arsenate reduction. The energy metabolism involving redox reactions of arsenic has been suggested to have evolved during early life on Earth. This review highlights the different systems evolved by prokaryotes to cope with arsenic and how they participate in its biogeochemical cycle.