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Direct, single-cell isolations of bacteria, primarily from natural, branching, waste water zoogloeas, were made by micromanipulation. Isolations were also made by conventional methods. Direct isolates were classified, chiefly with regard to zoogloea formation, into two groups designated group I (zoogloea-forming) and group II (nonzoogloea-forming). Casitone – glycerol – yeast autolysate agar medium was best for the isolation of group I bacteria. Group I isolates reduced nitrate to gas, possessed urease and catalase, and gave positive oxidase reactions. They were generally able to hydrolyze gelatin but, with one exception, did not produce acid from carbohydrates, and none produced H2S, indole, or acetylmethylcarbinol or utilized Koser citrate. Group II strains were usually more diverse on differential tests and could be distinguished from group I strains. Group I strains were characterized as Zoogloea strains and were found to be the predominant bacteria in natural, branching, zoogloeal colonies.

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An activated sludge from a sewage treatment plant and a laboratory activated sludge developed on an artificial waste were compared for their ability to utilize 11 aromatic compounds. There were several significant differences between them. The laboratory sludge contained higher numbers of organisms and metabolized the aromatics to a greater extent. Laboratory activated sludges acclimated to utilization of the aromatics differed from each other in population structure and the pattern of oxygen consumption with aromatic substrates. The oxidative patterns of uncontrolled mixed populations were unreliable for investigating metabolic pathways. Extracts of the various sludges elevated the plate counts of the sludges.