Bacterial class II catabolic transposons

Bacterial transposons encoding a variety of phenotypic traits are widelydisseminated in diverse species, thus allowing the host strains to expand their niches.Catabolic transposons responsible for the degradation of man-made and/or naturalorganic compounds provide the host cells to use these compounds as the sources ofcarbon, energy, and/or nitrogen, and have been identified worldwide in various bacterialstrains from the environments contaminated with herbicides, pesticides, petroleum, etc.Studies on these transposons have revealed that the catabolic genes for the compoundsare often located on the class II (Tn3-like) transposons, many of which are known tocarry resistance genes for antibiotics or heavy metals. In contrast to the insertionsequence (IS)-composite transposons, the class II transposons are able to transpose athigh frequencies even when they are large (>50 kb) in sizes, allowing the widedissemination of large gene clusters for the degradation of aromatic compounds such astoluene/xylenes, naphthalene, and carbazole. In the last two decades, we have identifiedmany class II catabolic transposons and clarified their structures, molecular functions,and in addition the entire sequences of large self-transmissible plasmids carrying thetransposons. In this review, we summarize the recent information on bacterial class IIcatabolic transposons, including their transposition mechanisms. Also described are theroles of these elements in establishment and evolution of the large catabolic plasmids.