Mobile elements as a combination of functional modules

Prokaryotic mobile elements have traditionally been classified as bacteriophages, plasmids, and transposons. We propose here a global classification of these and other bacterial and archaeal mobile elements based on their modular structure. This would allow for setting up interconnected databases where mobile elements could be stored as combinations of functional modules. Such a database would be very helpful. It would, for instance, allow for analyzing the phylogeny of individual blocks within an element, to understand how modules get associated and properly express the functions they carry in various bacterial hosts. Modules of practical importance, as for instance those that encode toxins or other virulence factors, could be identified and compared, and probes devised to test bacterial populations for the presence of such modules.