Ian Paulsen is a world leader in microbiology and a pioneer in microbial genomics. His work has focused on informatic followed by experimental characterisation of bacterial transport systems for nutrients and toxic compounds. He has discovered several novel classes of multidrug efflux pumps that can make bacteria resistant to multiple drugs by pumping them out of the cell. Paulsen’s work has revealed that these pumps have natural roles in the cell and have been opportunistically co-opted by hospital pathogens as a resistance mechanism against antibiotics. His global genome-based analyses have revealed fundamental strategic differences in transporters between single and multicellular lifeforms.