Production of 3,4-dihydroxybenzoic acid by Azomonas macrocytogenes and Azotobacter paspali

Abstract

Four strains of Azomonas macrocytogenes and a strain of Azotobacter paspali were found to produce a common extracellular, iron-binding, phenolic compound. This compound was purified from cell-free culture supernatant fluids and chemically identified as 3,4-dihydroxybenzoic acid (protocatechuic acid). 3,4-Dihydroxybenzoic acid was produced by cells growing in a simple defined medium containing acetate and glucose or sucrose as sole carbon sources. This compound promoted the solubilization of iron from the minerals olivine, glauconite, pyrite, and marcasite. Mineral-free medium prepared by preincubation with olivine or glauconite as the only iron source supported enhanced growth yields of Azomonas macrocytogenes (ATCC 12334) when 3,4-dihydroxybenzoic acid was present during the preincubation period. This suggests that 3,4-dihydroxybenzoic acid may play a role in solubilizing iron from some natural iron sources; however, 3,4-dihydroxybenzoic acid can not be considered a true siderophore since it was produced by Azomonas macrocytogenes and Azotobacter paspali growing in iron-limited and iron-sufficient medium.