Measurement of the uptake of radioactive para-aminobenzoic acid monitors folate biosynthesis in Escherichia coli K-12.

This study was undertaken to develop a method for rapidly and easily estimating the folate content of different strains of Escherichia coli. Cells were grown to stationary phase in medium containing radioactive para-aminobenzoic acid. The amount of label incorporated into cells was measured by collecting the cells on a filter, washing, and then determining the radioactivity retained on the filter. The addition of unlabeled para-aminobenzoic acid or the antifolate drugs sulfathiazole or trimethoprim reduced the uptake of the radioactive compound. These results indicate that uptake measurements monitored folate biosynthesis. The assay is well suited for the analysis of large numbers of samples and does not require specialized equipment.