Bacterial catabolic transposons

The introduction of foreign organic hydrocarbons into the environment in re cent years, as in the widespread use of antibiotics, has resulted in the ev olution of novel adaptive mechanisms by bacteria for the biodegradation of the organic pollutants. Plasmids have been implicated in the catabolism of many of these complex xenobiotics. The catabolic genes are prone to undergo genetic rearrangement and this is due to their presence on transposons or their association with transposable elements. Most of the catabolic transpo sons have structural features of the class I (composite) elements. These in clude transposons for chlorobenzoate (Tn5271), chlorobenzene (Tn5280), the newly discovered benzene catabolic transposon (Tn5542), and transposons enc oding halogenated alkanoates and nylon-oligomer-degradative genes. Transpos ons for the catabolism of toluene (Tn4651, Tn4653, Tn4656) and naphthalene (Tn4655) belong to class II (Tn3 family) elements. Many catabolic genes hav e been associated with insertion sequences, which suggests that these gene clusters could be rapidly disseminated among the bacterial populations. Thi s greatly expands the substrate range of the microorganisms in the environm ent and aids the evolution of new and novel degradative pathways. This enha nced metabolic versatility can be exploited for and is believed to play a m ajor part in the bioremediation of polluted environments.