Microbiology and biodegradation of resin acids in pulp mill effluents: a minireview.

Resin acids, a group of diterpenoid carboxylic acids present mainly in softwood species, are present in many pulp mill effluents and toxic to fish in recipient waters. They are considered to be readily biodegradable. However, their removal across biological treatment systems has been shown to vary. Recent studies indicate that natural resin acids and transformation products may accumulate in sediments and pose acute and chronic toxicity to fish. Several resin acid biotransformation compounds have also been shown to bioaccumulate and to be more resistant to biodegradation than the original material. Until recently, the microbiology of resin-acid degradation has received only scant attention. Although wood-inhabiting fungi have been shown to decrease the level of resin present in wood, there is no conclusive evidence that fungi can completely degrade these compounds. In contrast, a number of bacterial isolates have recently been described which are able to utilize dehydroabietic or isopimaric acids as their sole carbon source. There appears to be an unusually high degree of substrate specificity with respect of the utilization of abietane congeners and the presence of substituents. Pimaranes do not appear to be attacked to the same extent as the abietanes. This paper reviews the occurrence, chemistry, toxicity, and biodegradation of resin acids in relation to the biological treatment of pulp and paper mill effluents.

Growth, induction, and substrate specificity of dehydroabietic acid-degrading bacteria isolated from a kraft mill effluent enrichment.

We investigated resin acid degradation in five bacteria isolated from a bleach kraft mill effluent enrichment. All of the bacteria grew on dehydroabietic acid (DHA), a resin acid routinely detected in pulping effluents, or glycerol as the sole carbon source. None of the strains grew on acetate or methanol. Glycerol-grown, high-density, resting-cell suspensions were found to undergo a lag for 2 to 4 h before DHA degradation commenced, suggesting that this activity was inducible. This was further investigated by spiking similar cultures with tetracycline, a protein synthesis inhibitor, at various times during the DHA disappearance curve. Cultures to which the antibiotic was added prior to the lag did not degrade DHA. Those that were spiked with the antibiotic after the lag phase (4 h) degraded DHA at the same rate as did controls with no added tetracycline. Therefore, de novo protein synthesis was required for DHA biodegradation, confirming that this activity is inducible. The five strains were also evaluated for their ability to degrade other resin acids. All strains behaved in a similar fashion. Unchlorinated abietane-type resin acids (abietic acid, DHA, and 7-oxo-DHA) were completely degraded within 7 days, whereas pimarane resin acids (sandaracopimaric acid, isopimaric acid, and pimaric acid) were poorly degraded (25% or less). Chlorination of DHA affected biodegradation, with both 12,14-dichloro-DHA and 14-chloro-DHA showing resistance to degradation. However, 50 to 60% of the 12-chloro-DHA was consumed within the same period.

Differential fructose effect in Pachysolen tannophilus and Pichia stipitis.

The yeasts Pachysolen tannophilus and Pichia stipitis differed in their ability to utilize D-xylose in the presence of D-fructose. When P. tannophilus was grown aerobically in fructose-xylose mixture, the ketohexose was utilized preferentially over the pentose. However, in P. stipitis cultures, the converse was observed. The effect was associated with the ability of D-fructose to repress the induction of xylose reductase and xylitol dehydrogenase activities in P. tannophilus but not in P. stipitis. Both yeasts grew on D-fructose and fermented it to ethanol when it was supplied as the sole carbon source. The results suggest that there may exist some fundamental difference in the regulation of D-fructose metabolism between P. tannophilus and P. stipitis.