Phenanthrene degradation by microorganisms isolated from a contaminated stream. Environmental Pollution.

Abstract Autochthonous yeast and bacteria strains were isolated from a contaminated stream and studied for their potential to degrade phenanthrene, a three-ring polycyclic aromatic hydrocarbon (PAH), as their only source of carbon and energy. Rhodotorula glutinis and Pseudomonas aeruginosa were the prevailing microorganisms utilizing phenanthrene. Cells of these microorganisms were inoculated in liquid mineral basal medium at 25, 50, 100 and 200 mg phenanthrene liter À1 in ethanolic solution. To volatilize the ethanol the medium was dried for 40 min at 35 C with UV exposure. Almost complete phenanthrene degradation was observed during the 1-month incubation period. R. glutinis grew exponentially to a maximum of 9.5Â10 6 colony-forming units (CFUs) ml À1 , with a short lag time only at 200 mg liter À1 . The highest density (1.4Â10 7 CFU ml À1 ) without a lag time was obtained at 50 mg liter À1 ; lower cell numbers were observed at 25 and 100 mg liter 8 CFU ml À1 were observed in P. aeruginosa cultures at 50±100 mg liter À1 , respectively, on the 22nd day. At 25 and 200 mg liter À1 lower bacteria numbers were obtained (2.1±3.0Â10 8 CFU ml À1 ) on the 28th day. R. glutinis was as active as P. aeruginosa at growing on phenanthrene; the aromatic hydrocarbon degradation correlated directly to microbial density and biomass increase, the highest biomass reaching 238.0 and 50.0 mg liter À1 for the yeast and bacteria species, respectively.