Fig. 4.
An fmt null mutant is sensitive to citrate. (a) Representative photograph (from at least six replicates) of a disc diffusion assay with WT (CU1065), fmt mutant (HB21006) and fmt Pspac(hy)-fmt (HB21016) strains on LB plates. The discs were spotted with 10 µl of 1 M trisodium citrate (Na3C6H5O7) as indicated. (b) Growth of WT, fmt mutant and fmt Pspac(hy)-fmt (HB21016) strains on LBC plates (LB supplemented with 1g l−1 of sodium citrate) at 37 °C for 36 h. In this experiment, the discs were spotted with 10 µl of 1 M FeSO4. Note that the fmt mutant had a severe growth defect in this medium and could not form a lawn. Note also that there is better growth near the Fe-containing filter, suggesting that citrate may impose an Fe limitation. (c) Quantitation of sensitivity of WT and mutant strains to citrate using disc diffusion assay. The results are expressed as the diameter of the inhibition zone (mm) minus the diameter of the filter paper disc (6.5 mm).