An unusual Tn21-like transposon containing an ars operon is present in highly arsenic-resistant strains of the biomining bacterium Acidithiobacillus caldus

• Published in: Microbiology (Society for General Microbiology) Vol. 151; no. 9; pp. 3027 - 3039
• Main Authors: Tuffin, I. Marla, de Groot, Peter, Deane, Shelly M, Rawlings, Douglas E
• Format: Journal Article
• Language: English
• Published: Reading Soc General Microbiol 01.09.2005; Society for General Microbiology
• Subjects: Acidithiobacillus - drug effects; Acidithiobacillus - genetics; Acidithiobacillus - metabolism; Acidithiobacillus caldus; Arsenic - pharmacology; Bacteriology; Biodegradation, Environmental; Biological and medical sciences; Cloning, Molecular; DNA Transposable Elements - genetics; Drug Resistance, Bacterial; Escherichia coli; Fundamental and applied biological sciences. Psychology; Gene expression; Genetics; Microbiology; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Multienzyme Complexes; Operon; Transcription, Genetic; Polymerase chain reaction; Resistance; Pulsed field electrophoresis; Arsenic; Operon; Transposon; Bacteria; Transposable element; Strain
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/mic.0.28131-0

Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa Correspondence Douglas E. Rawlings der{at}sun.ac.za A transposon, Tn AtcArs , that carries a set of arsenic-resistance genes was isolated from a strain of the moderately thermophilic, sulfur-oxidizing, biomining bacterium Acidithiobacillus caldus . This strain originated from a commercial plant used for the bio-oxidation of gold-bearing arsenopyrite concentrates. Continuous selection for arsenic resistance over many years had made the bacterium resistant to high concentrations of arsenic. Sequence analysis indicated that Tn AtcArs is 12 444 bp in length and has 40 bp terminal inverted repeat sequences and divergently transcribed resolvase and transposase genes that are related to the Tn 21 -transposon subfamily. A series of genes consisting of arsR , two tandem copies of arsA and arsD , two ORFs (7 and 8) and arsB is situated between the resolvase and transposase genes. Although some commercial strains of At. caldus contained the arsDA duplication, when transformed into Escherichia coli , the arsDA duplication was unstable and was frequently lost during cultivation or if a plasmid containing Tn AtcArs was conjugated into a recipient strain. Tn AtcArs conferred resistance to arsenite and arsenate upon E. coli cells. Deletion of one copy of arsDA had no noticeable effect on resistance to arsenite or arsenate in E. coli . ORFs 7 and 8 had clear sequence similarity to an NADH oxidase and a CBS-domain-containing protein, respectively, but their deletion did not affect resistance to arsenite or arsenate in E. coli . Tn AtcArs was actively transposed in E. coli , but no increase in transposition frequency in the presence of arsenic was detected. Northern hybridization and reporter gene studies indicated that although ArsR regulated the 10 kb operon containing the arsenic-resistance genes in response to arsenic, ArsR had no effect on the regulation of genes associated with transposition activity. The GenBank/EMBL/DDBJ accession number for the nucleotide sequence of Tn AtcArs is AY821803 .