Anaerobically digested municipal sewage sludge which had been acclimated to monochlorophenol degradation for more than 2 years was shown to degrade pentachlorophenol (PCP). Di-, tri-, and tetrachlorophenols accumulated when PCP was added to the individual acclimated sludges. When the 2-chlorophenol-(2-CP), 3-CP-, and 4-CP-acclimated sludges were mixed in equal volumes, PCP was completely dechlorinated. The same results were obtained in sludge acclimated to the three monochlorophenol isomers simultaneously. With repeated PCP additions, 3,4,5,-trichlorophenol, 3,5-dichlorophenol, and 3-CP accumulated in less than stoichiometric amounts. All chlorinated compounds disappeared after PCP additions were stopped. All chlorinated compounds disappeared after PCP additions were stopped. Incubations with [14C]PCP resulted in 66% of the added 14C being mineralized to 14CO2 and 14CH4. Technical-grade PCP was found to be degraded initially at a rate very similar to that of reagent-grade PCP, but after repeated additions, the technical PCP was degraded more slowly. Pentabromophenol was also rapidly degraded by the mixture of acclimated sludges. These results clearly show the complete reductive dechlorination of PCP by the combined activities of three chlorophenol-degrading populations.

The degradation of seven chlorinated aromatic compounds in anaerobic sewage sludge from three Michigan communities was examined. The compounds tested were 2,4‐D (2,4‐dichlorophenoxy acetic acid), 2,4,5‐T (2,4,5‐trichlorophenoxy acetic acid), PCP (pentachlorophenol), 2,4,6‐trichlorophenol, and 2‐, 3‐, and 4‐chlorophenol. All of the compounds tested were degraded in one or more of the sludges during a 70‐d incubation period. Overall, 4‐chlorophenol was the most persistent compound tested followed by 3‐chlorophenol. The most rapid degradative reactions were cleavage of the ether linkage of the phenoxy acetic acid herbicides 2,4‐D and 2,4,5‐T, and the removal of Cl atoms ortho to the phenolic OH group of the chlorophenols. The initial products of 2,4‐D and 2,4,5‐T degradation were 4‐chlorophenol and 2,4,5‐trichlorophenol. Reductive dechlorination of 2,4,5‐trichlorophenol (produced from 2,4,5‐T) gave 3,4‐dichlorophenol and 4‐chlorophenol which were the final products of 2,4,5‐T degradation. Dechlorination of PCP gave 3,4,5‐trichlorophenol as the initial transformation product, and further dechlorination gave 3,5‐dichlorophenol as the final product of PCP degradation. The Jackson sludge had the greatest capacity to degrade the compounds tested. With the exception of 3‐ and 4‐chlorophenol, all other compounds tested were completely degraded in 7 to 14 d in the Jackson sludge. Mason and Adrian sludges were similar in their degradative pathways overall, but significantly less active than the Jackson sludge.

Dehalogenation of carbon tetrachloride, chloroform, and bromoform in pure cultures of Methanosarcina sp. strain DCM and Methanosarcina mazei S6 was demonstrated. The initial dechlorination product of chloroform was methylene chloride (dichloromethane), which accumulated transiently to about 70% of the added chloroform; trace amounts of chloromethane were also detected. The amount of chloroform dechlorinated per mole of methane produced was approximately 10 times greater than the ratio observed previously for tetrachloroethene dechlorination by these strains. The production of 14CO2 from [14C]chloroform and the absence of 14CH4 imply that processes in addition to reductive dechlorination operate.

We characterized bacteria from contaminated aquifers for their ability to utilize aromatic hydrocarbons under hypoxic (oxygen-limiting) conditions (initial dissolved oxygen concentration about 2 mg/l) with nitrate as an alternate electron acceptor. This is relevant to current intense efforts to establish favorable conditions for in situ bioremediation. Using samples of granular activated carbon slurries from an operating groundwater treatment system, we isolated bacteria that are able to use benzene, toluene, ethylbenzene, or p-xylene as their sole source of carbon under aerobic or hypoxic-denitrifying conditions. Direct isolation on solid medium incubated aerobically or hypoxically with the substrate supplied as vapor yielded 10(3) to 10(5) bacteria ml-1 of slurry supernatant, with numbers varying little with respect to isolation substrate or conditions. More than sixty bacterial isolates that varied in colony morphology were purified and characterized according to substrate utilization profiles and growth condition (i.e., aerobic vs. hypoxic) specificity. Strains with distinct characteristics were obtained using benzene compared with those isolated on toluene or ethylbenzene. In general, isolates obtained from direct selection on benzene minimal medium grew well under aerobic conditions but poorly under hypoxic conditions, whereas many ethylbenzene isolates grew well under both incubation conditions. We conclude that the conditions of isolation, rather than the substrate used, will influence the apparent characteristic substrate utilization range of the isolates obtained. Also, using an enrichment culture technique, we isolated a strain of Pseudomonas fluorescens, designated CFS215, which exhibited nitrate dependent degradation of aromatic hydrocarbons under hypoxic conditions.

No abstract