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

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 100 μg mL⁻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 24 h, a 40% decrease in Rhizobium growth was observed when exposed to 40 μg mL⁻¹ of either PHE or BaP. Furthermore, bacterial growth was completely inhibited by PHE or BaP applied in 80 and 100 μg mL⁻¹. After 96 h, the growth of R. tropici at 40 μg PHE mL⁻¹ or 60 μg BaP mL⁻¹ was similar to those treatments without PAH. To evaluate R. tropici degrading capabilities, supernatants of cultures with 40 μg PHE mL⁻¹ or 60 μg BaP mL⁻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 24 h, degradation obtained at 120 h 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.