Horizontal gene transfer and microbial adaptation to xenobiotics: new types of mobile genetic elements and lessons from ecological studies.

The characterization of bacteria that degrade organic xenobiotics has revealed that they can adapt to these compounds by expressing 'novel' catabolic pathways. At least some of them appear to have evolved by patchwork assembly of horizontally transmitted genes and subsequent mutations and gene rearrangements. Recent studies have revealed the existence of new types of xenobiotic catabolic mobile genetic elements, such as catabolic genomic islands, which integrate into the chromosome after transfer. The significance of horizontal gene transfer and patchwork assembly for bacterial adaptation to pollutants under real environmental conditions remains uncertain, but recent publications suggest that these processes do occur in a polluted environment.