Professor Reeves is internationally renowned for his genetic analysis of enteric bacteria. He determined the genetic basis of the enormous variation in O antigens. There can be more than a I00 forms within a species and little overlap even between related species. This variation is due to reassortment of genes between O antigen genes and other gene clusters, and transfer of gene clusters between species. He showed that the 7th pandemic clone of Vibrio cholerae did not arise directly from the 6th pandemic clone, suggesting-it arose from an environmental strain, with implications for the origins of this major human pathogen.