Microbial characterization and quantification of an anaerobic sludge degrading dimethyl phthalate.

AIMS: Characterization and quantification of microbial community in dimethyl phthalate (DMP)-degrading anaerobic sludge using molecular techniques.

METHODS AND RESULTS: An enriched anaerobic sludge effectively degrading over 99% of dimethyl phthalate in an upflow anaerobic sludge blanket (UASB) reactor for 530 days was characterized and quantified by 16S rRNA-based molecular methods. A total of 78 Bacteria clones were classified into 22 operational taxonomic units (OTUs) in nine divisions, including Firmicutes, Proteobacteria, Chloroflexi, Thermotogae, Bacteroidetes/Chlorobi, Spirochaetes, Acidobacteria and two candidate divisions. The two most abundant OTUs were likely responsible, respectively, for the de-esterification of DMP and the subsequent phthalate degradation. The outer layer of the granule was dominated by Bacteria; whereas the interior was by Archaea, of which 89 +/- 5% were acetoclastic Methanosaetaceae and 11 +/- 5% hydrogenotrophic Methanomicrobiales.

CONCLUSIONS: Twenty-two Bacteria OTUs in DMP-degrading anaerobic sludge distributed in nine divisions. The two most abundant OTUs were likely responsible respectively for the de-esterification of DMP and the subsequent phthalate degradation. Layered granular microstructure of DMP-degrading anaerobic sludge suggested that the rate of DMP de-esterification is faster than its inward diffusion rate.

SIGNIFICANCE AND IMPACT OF THE STUDY: This work is the first study to characterize and quantify the microbial community in the anaerobic phthalic ester degrading sludge from the anaerobic reactor.