The high degree of functional diversity of bacteria is in part a consequence of lateral gene transfer involving the inegron/gene cassette system. Without the need for all members of a population to possess the same complete set of genes, the cassette metagenome instead allows adaptive traits and functions to be rapidly distributed between individuals. This generates considerable genomic plasticity, giving rise to phenomena such as the rapid spread of antibiotic resistance and the wide range of virulence observed for some pathogens. We have recently established a structural genomics program based on a unique PCR probe of gene cassettes, allowing us to directly sample functions encoded within the mobile metagenome. The gene cassettes we have recovered from both cultured Vibrio strains and direct environmental sources provide a resource of considerable novelty and variety. A large fraction are ORFan genes or homologs of genes of unknown biological function, and structure elucidation therefore represents the sole route to ther functional annotation. I will describe progress with screening and production of our large panel of structural targets. The power of the approach will be demonstrated with reference to crystal structures solved to date, which define enzymes uniquely adapted for metabolising unusual structure. These include a variant of an α+β barrel fold enzyme, as will as a new member of te MazG family.