Plasmid-mediated bioaugmentation of activated sludge bacteria in a sequencing batch moving bed reactor using pNB2

The applicability of plasmid pNB2 for bioaugmentation of bacteria in model wastewater treatment reactors receiving 3-chloroaniline (3-CA) was investigated.

A setup of three biofilm reactors was studied, all initially inoculated with bacteria from activated sludge. Reactor PB received a Pseudomonas putida pNB2 donor strain not able to degrade 3-CA. Positive control reactor P received a 3-CA degrading Comamonas testosteroni pNB2-transconjugant. The negative control reactor N remained unchanged. Reactor P showed 3-CA degradation from the beginning of the experiment whereas in reactor PB, degradation started after an initial lag period. No degradation was observed in reactor N. PCR analysis showed that the P. putida donor abundance dropped in reactor PB, whereas the plasmid abundance did not, indicating transfer to other bacteria. A number of different 3-CA degrading C. testosteroni strains carrying pNB2 could be isolated from reactor PB.

A successful plasmid-mediated bioaugmentation was achieved with C. testosteroni being the dominant 3-CA degrading pNB2 transconjugant species active in reactor PB.

The study underlines the potential of gene transfer to contribute to establishment and spread of genetic information in general, particularly emphasizing the spread of xenobiotic degrading potential by dissemination of catabolic genes.