To test if cardiolipin is necessary to localize MurG to the forespore, we directly added purified cardiolipin to the strain with deleted cardiolipin synthesis genes (JDB2238). At T3 after initiation of sporulation, when MurG-YFP signal is first detected, a final concentration of 30 mM purified cardiolipin was added to sporulating cultures. We compared at different time points the localization pattern of MurG-YFP in the cardiolipin-null strain, wild type (JDB1689) and cardiolipin-null strain with added cardiolipin. Addition of cardiolipin to the cardiolipin-null strain rescues the main localization of MurG-YFP to the spore (Fig. 4C, S6). At its maximum, the spore to mother cell fluorescence ratio is 2.43 _ .18 for wild type cells (JDB1689), 1.59 _ .14 for the mutant strain (JDB2238) and 2.16 _ .18 for the mutant strain with added cardiolipin (Fig. 4D). Thus, images and quantification of the localization demonstrate that cardiolipin is necessary to localize MurG-YFP to the forespore and restore its wild type distribution.