Biodegradation of p-hydroxybenzoic acid in Herbaspirillum aquaticum KLS-1 isolated from tailing soil: Characterization and molecular mechanism

The wide distribution of p-hydroxybenzoic acid (PHBA) in the environments has attracted great concerns due to its potential risks to organisms. Bioremediation is considered a green way to remove PHBA from environment. Here, a new PHBA-degrading bacterium Herbaspirillum aquaticum KLS-1was isolated and its PHBA degradation mechanisms were fully evaluated. Results showed that strain KLS-1 could utilize PHBA as the sole carbon source and completely degrade 500 mg/L PHBA within 18 h. The optimal conditions for bacterial growth and PHBA degradation were pH values of 6.0-8.0, temperatures of 30 °C-35 °C, shaking speed of 180 rpm, Mg2+ concentration of 2.0 mM and Fe2+ concentration of 1.0 mM. Draft genome sequencing and functional gene annotations identified three operons (i.e., pobRA, pcaRHGBD and pcaRIJ) and several free genes possibly participating in PHBA degradation. The key genes pobA, ubiA, fadA, ligK and ubiG involved in the regulation of protocatechuate and ubiquinone (UQ) metabolisms were successfully amplified in strain KLS-1 at mRNA level. Our data suggested that PHBA could be degraded by strain KLS-1 via the protocatechuate ortho-/meta-cleavage pathway and UQ biosynthesis pathway. This study has provided a new PHBA-degrading bacterium for potential bioremediation of PHBA pollution.