Gene Mobilization Moves Genes from the Chromosome to a Plasmid

Mobilization has been studied extensively with genes encoding proteins that break down ß-lactams, such as penicillin. After mobilization, the genes encoding ß-lactamases continue to evolve. For some types, it has been possible to identify hundreds of varieties that originally came from one or a few mobilization events. Consequently, good evidence exists for mobilization leading to gene movement among species. Gene mobilization is part of the reason that indiscriminate antibiotic use is so dangerous: Emergence of resistance in commensal bacteria (see Box 6-3) can serve as a starting point for mobilization of resistance that eventually reaches pathogens.