Effect of robA
overexpression on organic solvent tolerance. Cultures of Y. pestis (Yp) and E. coli (Ec) strains carrying the plasmids indicated were spotted on solid medium. The surface of the medium was overlaid with the organic solvent and growth was recorded after incubation. H, n-hexane; CH, cyclohexane; P, n-pentane; X, p-xylene; DE, diphenyl ether; -, no solvent control.