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Characterization and enumeration of the resin acid-degrading bacterial population of a sequencing batch reactor: an emphasis on the isopimaric acid-degrading bacteria Wilson, Ann Elise-Jordan


Resin acids are naturally occurring compounds produced by conifers and released by pulp and paper mills. These compounds are problematic to papermaking processes and are highly toxic to aquatic organisms. Since basic microbial research on biodegradation of resin acids is limited, it was of interest to investigate the resin acid-degrading community of an established sequencing batch reactor operated at temperatures between 20° and 50°C; to determine if operating temperature changes affected the species present. Specificities for resin acids and other substrates, temperature ranges for and induction of resin acid degradation were characterized for several isolates. Five resin acid-degrading bacterial strains were isolated from the sequencing batch reactor at either 20° or 40°C. AbA-1 grew on the abietanes, dehydroabietic and abietic acids. IpA-1, IpA-2, IpA-13, and AbA-5 grew on the pimaranes, isopimaric and pimaric acids, and the above abietanes. These latter four strains are the first reported isolates which grow on the pimaranes as a sole organic carbon and energy sources. Carbon mass balance determinations for IpA-1, IpA-2 and IpA-13 could not conclusively prove that isopimaric acid was completely mineralized because one-third of the isopimaric acid carbon remained as dissolved organic carbon; however, partial mineralization was shown. IpA-1 did not produce a biosurfactant during growth on isopimaric acid. Induction studies confirmed removal of resin acids by isopimaric acid degraders requires induction by growth on IpA. When the five strains were compared biochemically, the results suggested that increasing the temperature of the sequencing batch reactor from 20° to 40°C changed the resin aciddegrading bacterial community, from one with at least two gram-negative populations, abietane and pimarane-degrading ones, to a less diverse one with a gram-positive population having the ability to remove both abietanes and pimaranes. Most probable number determinations showed increasing the reactor's temperature above 40°C decreased the culturable isopimaric, dehydroabietic, and abietic acid-degrading populations to 103 per 100 ml. The remaining populations above 40°C required additional energy sources to remove resin acids. The resin acid-degrading community was resilient to rapid changes in resin acid concentration up to 3000 pM and pH shifts to 6 or 8.

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