OPERATION PARAMETERS AFFECTING THE SURVIVAL OF GENETICALLY-ENGINEERED MICROORGANISMS IN ACTIVATED-SLUDGE PROCESSES

The survival of genetically engineered microorganisms (GEMs) harboring recombinant plasmid pBH500, containing catechol 2,3-oxygenase encoding gene, in model activated sludge processes was investigated. Escherichia coli C600 (pBH500) and Pseudomonas putida BH(pBH500) were inoculated into activated sludge and cultivated in the fill and draw (FD) and continuous how (CF) systems under different conditions. In both systems, the populations of introduced GEMs declined rapidly during the initial period (5-10 days for the FD system and 5-15 days for the CF system), after which they remained relatively stable. In the FD system, the larger the inoculum size, the higher the population level at which the GEMs remained stable. However, in the CF system, repeated inoculation did not improve the survival of P. putida BH(pBH500). The sludge retention time (SRT) affected the survival of GEMs considerably in both systems; as the SRT of the system was decreased, the survival populations of GEMs increased. The presence of phenol, which can support the growth of P. putida BH(pBH500), did not influence its survival.