Tolerance, growth and degradation of phenanthrene and benzo[a]pyrene by Rhizobium tropici CIAT 899 in liquid culture medium

Abstract

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous pollutants that are toxic and recalcitrant to degradation by bacteria. This research evaluated the toxicity of different concentrations [10, 20, 40, 60, 80 and 100μgmL-1] of phenanthrene (PHE) or benzo[a]pyrene (BaP) on the growth of Rhizobium tropici CIAT899 under in vitro conditions as well as the potential degradation of PHE and BaP by this bacterium. At 24h, a 40% decrease in Rhizobium growth was observed when exposed to 40μgmL-1 of either PHE or BaP. Furthermore, bacterial growth was completely inhibited by PHE or BaP applied in 80 and 100μgmL-1. After 96h, the growth of R. tropici at 40μg PHEmL-1 or 60μg BaPmL-1 was similar to those treatments without PAH. To evaluate R. tropici degrading capabilities, supernatants of cultures with 40μg PHEmL-1 or 60μg BaPmL-1 were analyzed by gas chromatography coupled to mass spectrophotometer (GC-MS). R. tropici was able to degrade either PHE or BaP diminishing its concentration in 20% and 25% during the first 24h, degradation obtained at 120h was 50% and 45% for PHE or BaP, respectively. This research shows for the first time that R. tropici CIAT 899 grows in liquid culture medium contaminated with PAH, and moreover is able to growth and to degrade either PHE or BaP. Show more