BACKGROUND AND OBJECTIVES Phthalates are synthetic compounds widely used as plasticizers in various industries. Microorganisms, particularly bacteria, have demonstrated the ability to metabolize the hazardous phthalates. Activated sludge; a mixture of microorganisms commonly used in wastewater treatment plants, has been found to harbor diverse microbial communities with the capability to degrade a wide range of pollutants. The aims of this study were isolation and characterization of phthalate degrading bacteria from activated sludge in petrochemical plant. MATERIALS AND METHODS Activated sludge samples were collected from a wastewater treatment plant. About 7 mL of the collect samples was inoculated into 100 mL enrichment medium contains mineral salt medium (MSM) supplemented with 0.5 g L-1 carbon of each dimethyl phthalate (DMP) or dibutyl phthalate (DBP) as sole carbon and energy source. The flasks were incubated on an orbital shaker at 30 °C, 120 rpm, pH 7±0.2 during 2-7 days. The bacterial degradation activity was determined using a spectrophotometer at 600 nm. The enriched cultures were plated out on selective agar to isolate individual phthalate degrading bacteria. The isolates were further characterized based on morphological, biochemical, and molecular techniques. RESULTS AND DISCUSSION Among 11 isolates, two Gram negative bacteria named MAF1 and MAF11 were degraded both phthalates as a sole carbon and energy source. The results showed that degradation of DMP and DBP by MAF1 and MAF11 were initiated after 12 hours then reached to a maximum after 48 and 120 hours incubation, respectively. In addition, the optical density assay in growth cultures contains DMP and DBP for both isolates were increased from 0.026 to 0.276 and 0.27 to 0.473, respectively. CONCLUSION The results demonstrated two bacteria isolated from activated sludge were able to degrade phthalates. These results revealed that both isolates are suitable for degradation of phthalates in industrial wastewater and contaminated sites.
