CLONING AND SEQUENCING SHOW THAT 4-HYDROXYBENZOATE HYDROXYLASE (POBA) IS REQUIRED FOR UPTAKE OF 4-HYDROXYBENZOATE IN RHIZOBIUM-LEGUMINOSARUM

Mutants of Rhizobium leguminosarum bv. viciae MNF300 and R. leguminosarum bv. trifolii WU95 unable to accumulate 4-hydroxybenzoate lack 4-hydroxybenzoate hydroxylase. The capacity of these mutants to take up and grow on 4-hydroxybenzoate was restored by a 2.0 kb EcoRI-PstI DNA fragment. This contained only one ORF which had over 60% DNA sequence similarity with the structural gene for 4-hydroxybenzoate hydroxylase (pobA) from Pseudomonas spp. and Acinetobacter. Reported effects of metabolic inhibitors and substrate analogues on the apparent uptake of 4-hydroxybenzoate have now been shown to be due to their direct effect on 4-hydroxybenzoate hydroxylase. We propose that uptake of 4-hydroxybenzoate is via a metabolic 'drag' mechanism dependent on the activity of the pobA gene product.