Ng Shee Ping, Davis Belinda, Palombo Enzo A, Bhave Mrinal
Environment and Biotechnology Centre, Faculty of Life and Social Sciences, Swinburne University of Technology, PO Box 218, Melbourne, Victoria 3122, Australia.
BMC Res Notes. 2009 Mar 7;2:38. doi: 10.1186/1756-0500-2-38.
Achromobacter sp. AO22 (formerly Alcaligenes sp. AO22), a bacterial strain isolated from a lead-contaminated industrial site in Australia, was previously found to be resistant to moderate to high levels of mercury, copper and other heavy metals. However, the nature and location of the genetic basis for mercuric ion resistance in this strain, had not been previously identified.
Achromobacter sp. AO22 contains a functional mer operon with all four essential genes (merRTPA) and shows >99% DNA sequence identity to that of Tn501. The mer operon was present on a transposon, designated TnAO22, captured by introducing a broad-host-range IncP plasmid into Achromobacter sp. AO22 and subsequently transferring it to E. coli recipients. The transposition frequency of TnAO22 was 10-2 to 10-3 per target plasmid transferred. Analysis of TnAO22 sequence revealed it belonged to the Tn21 subgroup of the Tn3 superfamily of transposons, with the transposition module having >99% identity with Tn5051 of a Pseudomonas putida strain isolated from a water sample in New York.
TnAO22 is thus a new variant of Tn5051 of the Tn3 superfamily and the transposon and its associated mercury resistance system are among the few such systems reported in a soil bacterium. Achromobacter sp. AO22 can thus be exploited for applications such as in situ mercury bioremediation of contaminated sites, or the mobile unit and mer operon could be mobilized to other bacteria for similar purposes.
无色杆菌属AO22菌株（以前称为产碱菌属AO22菌株），是从澳大利亚一个铅污染的工业场地分离出的细菌菌株，先前发现它对中度至高水平的汞、铜和其他重金属具有抗性。然而，该菌株中汞离子抗性的遗传基础的性质和位置此前尚未确定。
无色杆菌属AO22菌株含有一个具有所有四个必需基因（merRTPA）的功能性汞操纵子，并且与Tn501的DNA序列同一性大于99%。汞操纵子存在于一个转座子上，命名为TnAO22，通过将一个广泛宿主范围的IncP质粒引入无色杆菌属AO22菌株，随后将其转移到大肠杆菌受体中而捕获。TnAO22的转座频率为每转移一个靶质粒10-2至10-3。对TnAO22序列的分析表明，它属于转座子Tn3超家族的Tn21亚组，其转座模块与从纽约水样中分离出的恶臭假单胞菌菌株的Tn5051具有大于99%的同一性。
因此，TnAO22是Tn3超家族的Tn5051的一个新变体，并且该转座子及其相关的汞抗性系统是在土壤细菌中报道的少数此类系统之一。无色杆菌属AO22菌株因此可用于诸如对污染场地进行原位汞生物修复等应用，或者该移动单元和汞操纵子可被转移到其他细菌以用于类似目的。
