PHENANTHRENE DEGRADATION BY MICROORGANISMS ISOLATED FROM A CONTAMINATED STREAM

Autochthonous yeast and bacteria strains were isolated from a contamin ated stream and studied for their potential to degrade phenanthrene, a three-ring polycyclic aromatic hydrocarbon (PAH), as their only sourc e of carbon and energy. Rhodotorula glutinis and Pseudomonas aeruginos a 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(-1) in ethanolic solution. To volatilize the ethanol the medium was dried for 40 min at 35 degree s C with UV exposure. Almost complete phenanthrene degradation was obs erved during the 1-month incubation period. R. glutinis grew exponenti ally to a maximum of 9.5x10(6) colony-forming units (CFUs) ml(-1), wit h a short lag time only at 200 mg liter(-1). The highest density (1.4x 10(7) CFU ml(-1)) without a lag time was obtained at 50 mg liter(-1); lower cell numbers were observed at 25 and 100 mg liter(-1). During th e logarithmic phase the specific growth rate (mu) was 0.022 h(-1) and the corresponding doubling time (t(d)) was 31.5 h (50 mg liter(-1)). A reduction to one-tenth of cell yeast numbers was observed at the lowe st PAH levels on the 28th incubation day and a decrease of 100-fold wa s observed at 200 mg liter(-1). Higher mu-values (mu=d [In x/x(0)]/dt) , shorter t(d) (t(d)=[In 2]/mu), and a maximum of 7.7-7.4x10(8) CFU ml (-1) were observed in P. aeruginosa cultures at 50-100 mg liter(-1), r espectively, on the 22nd day. At 25 and 200 mg liter(-1) lower bacteri a numbers were obtained (2.1-3.0x10(8) CFU ml(-1)) on the 28th day. R. glutinis was as active as P. aeruginosa at growing on phenanthrene; t he aromatic hydrocarbon degradation correlated directly to microbial d ensity and biomass increase, the highest biomass reaching 238.0 and 50 .0 mg liter(-1) for the yeast and bacteria species, respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.