Identification of a new gene, molR, essential for utilization of molybdate by Escherichia coli

A mutation in a new gene, molR, prevented the synthesis in Escherichia coli of molybdoenzymes, including the two formate dehydrogenase isoenzymes, nitrate reductase and trimethylamine-N-oxide reductase. This phenotype was suppressed by supplementing the media with molybdate. Thus, the molR mutant was phenotypically similar to previously described chlD mutants, thought to be defective in molybdate transport. The molR gene is located at 65.3 min in the E. coli chromosome, in contrast to the chlD gene, which maps at 17 min and thus can be readily distinguished. The molR gene is also cotransducible with a hitherto unidentified gene essential for the production of 2-oxoglutarate from isocitrate, designated icdB (located at 66 min). The molR mutant strain SE1100 also failed to produce the hydrogenase component of formate hydrogenlyase (HYD3) in molybdate-unsupplemented media. The amount of molybdate required by strain SE1100 for the production of parental levels of formate hydrogenlyase activity was dependent on the growth medium. In Luria-Bertani medium, this value was about 100 microM, and in glucose-minimal medium, 1.0 microM was sufficient. In low-sulfur medium, this value decreased to about 50 nM. The addition of sulfate or selenite increased the amount of molybdate needed for the production of formate hydrogenlyase activity. These data suggest that in the absence of the high-affinity molybdate transport system, E. coli utilizes sulfate and selenite transport systems for transporting molybdate, preferring sulfate transport over the selenite transport system.