H. pylori phosphoribosyltransferase mutants show potential substrate specificities. OD600 values for 24-h growth assays of H. pylori strain G27 Δapt (A), Δapt rdxA::apt (B), and Δgpt rdxA::gptEC (C) phosphoribosyltransferase mutants in RnP medium containing only single purine bases or nucleoside sources. Bars indicate growth of designated mutants (black) and, when applicable, complemented mutant strains (white). Starting OD600 values were between 0.03 and 0.04. Error bars represent the standard errors of the means. N/A, no additive.