APPLIED GENETICS AND MOLECULAR BIOTECHNOLOGY Novel gene clusters involved in arsenite oxidation and resistance in two arsenite oxidizers: Achromobacter sp. SY8 and Pseudomonas sp. TS44 Lin Cai & Christopher Rensing & Xiangyang Li & Gejiao Wang Received: 6 January 2009 / Revised: 21 February 2009 / Accepted: 23 February 2009 / Published online: 13 March 2009 # Springer-Verlag 2009 Abstract This study describes three gene clusters involved in arsenic redox transformation of two arsenite oxidizers: Achromobacter sp. SY8 and Pseudomonas sp. TS44. A 17.5-kb sequence containing the arsenite oxidase (aox) gene cluster (aoxX-aoxS-aoxR and aoxA-aoxB-aoxC-aoxD) was isolated from SY8 using a fosmid library approach. Similarly, a 14.6-kb sequence including the aox cluster (arsD- arsA-aoxA-aoxB) and the arsenic resistance (ars) gene cluster (arsC1-arsR-arsC2-ACR3-arsH-dual specificity phosphatase (DSP)-glyceraldehyde-3-phosphate dehydroge- nase (GAPDH)-major facilitator superfamily (MFS)) was obtained from TS44 by inverse polymerase chain reaction (PCR). According to reverse transcription (RT) PCR experi- ments, SY8 aoxXSR and aoxABCD transcribed as two different transcripts in opposite directions, and TS44 aox and ars clusters transcribed as a single transcript in their respective cluster. All of these genes were found to be upregulated by the addition of arsenite [As(III)], arsenate [As (V)], and antimonite [Sb(III)], except that TS44 arsC1-arsR appeared to be expressed constitutively. The SY8 aox cluster was predicted to be regulated by a two-component signal transduction system and a potential regulatory model was proposed. The TS44 aox cluster is unusual since it contains structural genes only and arsDA in its upstream. The TS44 ars cluster includes several genes previously identified not associated with arsenic resistance or transformation. This study showed novel structures and arrangements of arsenic gene clusters associated with bacterial As(III) oxidation and As(V) reduction. Keywords Arsenic . Arsenite oxidizer . aox cluster . ars cluster Introduction Arsenic is recognized as one of the most toxic oxyanion in the natural environment, which caused severe contamina- tion of soil–water systems and subsequent endemic arsen- icosis in many countries, especially in Bangladesh, India, and China. Many microorganisms have evolved different arsenic detoxification pathways to cope with the wide- spread distribution of the poisonous arsenic (Rosen 2002). Four distinct microbial arsenic resistance mechanisms have previously been described: (1) As(III) oxidation, (2) cyto- plasmic As(V) reduction and As(III) extrusion, (3) respira- tory As(V) reduction, and (4) As(III) methylation (Qin et al. 2006; Silver and Phung 2005). These mechanisms confer arsenic resistance in microorganisms that play an important role in the transformation and geological cycle of arsenic. An ever increasing number of As(III)-oxidizing bacteria have been detected and studied including Alcaligenes faecalis (Philips and Taylor 1976), Agrobacterium tumefa- ciens 5A (Kashyap et al. 2006), Thiomonas sp. 3As (Duquesne et al. 2008), Herminiimonas arsenicoxydans ULPAs1 (Muller et al. 2007), and Thermus sp. HR13 (Gihring et al. 2001), etc. These strains can oxidize As(III) to the less toxic As(V) by As(III) oxidase. It is noteworthy to point out that two types of arsenite oxidizers exist in the environment. One type is able to use As(III) as the sole Appl Microbiol Biotechnol (2009) 83:715–725 DOI 10.1007/s00253-009-1929-4 L. Cai : X. Li : G. Wang (*) State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China e-mail: gejiaow@yahoo.com.cn C. Rensing Department of Soil, Water and Environmental Science, The University of Arizona, Tucson, AZ 85721, USA