PLASMID TRANSFER BETWEEN STRAINS OF PSEUDOMONAS-PUTIDA, AND THEIR SURVIVAL, WITHIN A PILOT-SCALE PERCOLATING-FILTER SEWAGE-TREATMENT SYSTEM

The ability of non-indigenous bacteria to survive and conjugate within a fully functioning pilot-scale percolating filter bed, with a substa ntial biofilm and a diverse invertebrate community, was investigated. Pseudomonas putida UWC8, harbouring the conjugative plasmid pQKH6, iso lated from river epilithon, and P. putida UWC9 were introduced and sur vived in a culturable state for up to 145 days. During this time plasm id transfer, with transfer frequencies of up to 6.54 X 10(-5) cfu per recipient, could be detected. The macro-invertebrate community was als o investigated. The invertebrate grazers had no detectable effect upon the densities of the introduced bacteria.