title: Stable augmentation of activated sludge with foreign catabolic genes harboured by an indigenous dominant bacterium.
abstract: Comamonas sp. rN7 is a phenol-degrading bacterium that represents the dominant catabolic population in activated sludge. The present study examined the utility of this bacterium for establishing foreign catabolic genes in phenol-digesting activated sludge. The phc genes coding for phenol hydroxylase and its transcriptional regulators of C. testosteroni R5 were integrated into the chromosome of strain rN7. The specific phenol-oxygenating activity of a resultant transformant designated rN7(R503) was three times higher than the activity of strain rN7, and the phc genes were stably inherited by rN7(R503) grown in a non-selective laboratory medium. Inoculation of phenol-acclimatized activated sludge with rN7(R503) resulted in a high phenol-oxygenating activity and improved resistance to phenol-shock loading compared to sludge inoculated with either no cells, rN7 or R5. Quantitative competitive polymerase chain reaction (PCR) showed that the phc genes were retained in the rN7(R503)-inoculated sludge at a density of more than 108 copies per ml of mixed liquor for more than 35 days, whereas those in the R5-inoculated sludge disappeared rapidly. No transfer of the phc genes to other indigenous populations was apparent in the rN7(R503)-harbouring sludge. From these results, we concluded that the phenol treatment of the activated sludge was enhanced by the phc genes harboured by the rN7(R503) population. This study suggests a possible bioaugmentation strategy for stably utilizing foreign catabolic genes in natural ecosystems.
mesh_terms: D001673:Biodegradation, Environmental; D002384:Catalysis; D020585:Comamonas / Q000235:genetics*; D005798:Genes, Bacterial; D005818:Genetic Engineering; D006899:Mixed Function Oxygenases / Q000235:genetics; D019800:Phenol / Q000378:metabolism*; D012037:Refuse Disposal; D012722:Sewage / Q000382:microbiology*
chemical_list: D012722:Sewage; D019800:Phenol; D006899:Mixed Function Oxygenases; C022336:phenol 2-monooxygenase