Conservation of mercury resistance determinants amongst ICE-like mobile bacterial genetic elements: comparative analysis and dissection of function

Enterobacterial Integrative Conjugative Elements (ICEs) are now detected regularly as carriers of drug resistance and adaptive functions in clinical, animal and environmental bacterial isolates. The elements, which appear as conjugative phage/ plasmid- like hybrids, have a core genetic structure comprising of integrative, regulatory and conjugative transfer functions. Several integrative hotspots within the elements have been characterised where genes from host organisms or transposonassociated elements integrate resulting in evolution of the ICE element itself. One such ICE integrating hotspot, originally characterised in the ICER391, contains a mercury resistance determinant. Bioinformatic analysis of several ICE elements has revealed the conservation of similar mercury resistance determinants amongst ICE elements from a wide geographical origin. Here we compare and characterise this ICER391 mercury resistant determinant and use molecular and bioinformatic analysis to delineate its structure, possible origin and function