Horizontal arsC gene transfer among microorganisms isolated from arsenic polluted soil Maria F. Villegas-Torres a , Oscar C. Bedoya-Reina a , Camilo Salazar b , Martha J. Vives-Florez a , Jenny Dussan a, * a Centro de Investigaciones Microbiológicas (CIMIC), Universidad de los Andes, Carrera 1 N  18A-12 Bogota, Colombia b Instituto de Genética, Universidad de los Andes, Carrera 1 N  18A-12 Bogota, Colombia article info Article history: Received 20 May 2010 Received in revised form 22 October 2010 Accepted 22 October 2010 Available online 18 November 2010 Keywords: Arsenate arsC Gene Indigenous microorganisms Horizontal gene transfer (HGT) abstract The study of recent evolution of the arsC genes amplified from microorganisms inhabiting a Colombian oil-polluted soil with high concentrations of arsenic was performed through the isolation of 26 bacterial morphotypes resistant to 10 mM of arsenate. A 353 bp fragment of the gene coding for arsenate- reductase enzyme (i.e. arsC), and a 500 bp 16S rDNA partial sequence were sequenced for 16 morpho- types of the 26 previously isolated. arsC sequences clustered on the same clade with previously reported arsC chromosomal genes of Escherichia coli and Shigella sp.; while 16S rDNA sequences grouped within the genus Pseudomonas and Bacillus. The GC content and the Codon Adaptation Index (CAI) were calculated and statistically compared, both supported the previous results. The IsolationeMigration model (IM model) was applied to calculate the genetic flux between each clade defined by the phylo- genetic analysis. In general, the existence of recent horizontal gene transfer (HGT) events was confirmed, and the presence of the arsC gene in Bacillus sphaericus is reported for the first time. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Arsenic is a heavy metal readily available in the environment in small quantities. Normally it is delivered by geochemical processes, but petroleum and mineral exploration increases its local concen- tration over the normal expectations (Mukhopadhyay et al., 2002). Arsenic binds the sulfhydryl groups of proteins causing an imme- diate inactivation resulting on a highly toxic effect for eukaryote and prokaryote cells (Belluck et al., 2003). In response to this selective pressure, microorganisms have developed different resistance mechanisms which include a wide arsenal of proteins for both arsenic reduction and oxidation (Mukhopadhyay et al., 2002). The origin of arsenate reduction mechanisms has been explained under two perspectives. The first proposes that they appeared by convergent evolution and were then fixed onto three clades (Mukhopadhyay et al., 2002); and the second states that a unique mechanism was originated in a common ancestor and was then horizontally transferred onto these clades (Jackson and Dugas, 2003). The first clade has been typified as arsC gluta- thioneeglutaredoxin dependent (arsC-GSH/Grx) and was identified in enteric bacteria (e. g. Escherichia coli); the second one is known as arsC tioredoxin dependent (arsC-Trx) and was found in Gram- positive bacteria (e.g. Staphylococcus). The final clade which include the arr2 gene, was amplified from Saccharomyces cerevisiae (Mukhopadhyay et al., 2002). Horizontal gene transfer (HGT) is a mechanism of gene dispersal between genus and domains, (Syvanen, 1985; Dufraigne et al., 2005), and has a major importance in fitness of bacteria inhabit- ing polluted habitats (Herrick et al., 1997; Springael and Top, 2004; Martinez et al., 2006). The events of HGT occur as a mechanism of environmental adaptability (Nemergut et al., 2004). This might be favored by environmental pollution, such as the occurrence of high concentration of heavy metals, like arsenic (Cai et al., 2009; Cavalca et al., 2010). In order to design better strategies for bioremediation of arsenic polluted soils, it is important to identify the mechanisms that indigenous bacteria are using to overcome the toxic effects, and the mechanisms by which they spread in the environment. As a first approach to establish a proper detoxification methodology for Colombian arsenic polluted soils, we study the recent evolution of arsC genes from indigenous bacteria inhabiting the soils under study. Using phylogenetical inference, statistical comparisons of the GC contents, CAI, and migration rate parameters, the results of this study suggest the HGT of arsC genes between the isolated morphotypes from arsenic polluted soils. * Corresponding author. Jenny Dussan, Lab 207, Centro de Investigaciones Microbiológicas (CIMIC), Universidad de los Andes, Carrera 1 N  18A-10 Bogota, Colombia. Tel.: þ57 571 339 4949x2767; fax: þ57 571 332 4368. E-mail address: jdussan@uniandes.edu.co (J. Dussan). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod 0964-8305/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2010.10.007 International Biodeterioration & Biodegradation 65 (2011) 147e152