Enrichment and immobilization of quinone-respiring bacteria in anaerobic granular sludge.

The capacity of an anaerobic granular sludge for serving as an immobilizing mechanism for quinone-respiring bacteria was evaluated. The inoculum was continuously fed with a basal medium containing the humic model compound, anthraquinone-2,6-disulfonate (AQDS), as a terminal electron acceptor. Complete reduction of AQDS was achieved by the granular sludge for a prolonged period in an anaerobic bioreactor provided with a mixture of volatile fatty acids as a substrate. Phylogenetic analysis revealed the enrichment and immobilization of AQDS-respiring bacteria appearing as dominant organisms in the microbial population of the AQDS-supplemented reactor, compared to a reactor control operated under methanogenic conditions. The consistent quinone-reducing capacity observed in the consortium indicates that it is feasible to apply quinone-reducing microorganisms in continuous bioreactors and this ability can potentially be important in wastewaters rich in humic substances. The quinone reducing activity could also be applied to accelerate the conversion of xenobiotics susceptible to reductive biotransformations such as azo dyes and polychlorinated compounds in continuous bioreactors.

Anaerobic mineralization of toluene by enriched sediments with quinones and humus as terminal electron acceptors.

The anaerobic microbial oxidation of toluene to CO(2) coupled to humus respiration was demonstrated by use of enriched anaerobic sediments from the Amsterdam petroleum harbor (APH) and the Rhine River. Both highly purified soil humic acids (HPSHA) and the humic quinone moiety model compound anthraquinone-2,6-disulfonate (AQDS) were utilized as terminal electron acceptors. After 2 weeks of incubation, 50 and 85% of added uniformly labeled [(13)C]toluene were recovered as (13)CO(2) in HPSHA- and AQDS-supplemented APH sediment enrichment cultures, respectively; negligible recovery occurred in unsupplemented cultures. The conversion of [(13)C]toluene agreed with the high level of recovery of electrons as reduced humus or as anthrahydroquinone-2,6-disulfonate. APH sediment was also able to use nitrate and amorphous manganese dioxide as terminal electron acceptors to support the anaerobic biodegradation of toluene. The addition of substoichiometric amounts of humic acids to bioassay reaction mixtures containing amorphous ferric oxyhydroxide as a terminal electron acceptor led to more than 65% conversion of toluene (1 mM) after 11 weeks of incubation, a result which paralleled the partial recovery of electron equivalents as acid-extractable Fe(II). Negligible conversion of toluene and reduction of Fe(III) occurred in these bioassay reaction mixtures when humic acids were omitted. The present study provides clear quantitative evidence for the mineralization of an aromatic hydrocarbon by humus-respiring microorganisms. The results indicate that humic substances may significantly contribute to the intrinsic bioremediation of anaerobic sites contaminated with priority pollutants by serving as terminal electron acceptors.