ACTIVITY AND STABILITY OF A RECOMBINANT PLASMID-BORNE TCE DEGRADATIVEPATHWAY IN BIOFILM CULTURES

The activity and stability of the TCE degradative plasmid TOM31c in th e transconjugant host Burkholderia cepacia 17616 was studied in select ive and non-selective biofilm cultures. The activity of plasmid TOM31c in biofilm cultures was measured by both TCE degradative studies and the expression of the Tom pathway. Plasmid loss was measured using con tinuous flow, rotating annular biofilm reactors, and various analytica l and microbiological techniques. The probability of plasmid loss in t he biofilm cultures was determined using a non-steady-state biofilm pl asmid loss model that was derived from a simple mass balance, incorpor ating results from biofilm growth and plasmid loss studies. The plasmi d loss model also utilized Andrew's inhibition growth kinetics and a b iofilm detachment term. Results from these biofilm studies were compar ed to similar studies performed on suspended cultures of Burkholderia cepacia 17616-TOM31c to determine if biofilm growth has a significant effect on either plasmid retention or Tom pathway expression (i.e., TC E degradation rates). Results show that the activity and expression of the Tom pathway measured in biofilm cultures was significantly less t han that found in suspended cultures at comparable growth rates. The d ata obtained from these studies fit the plasmid loss model well, provi ding plasmid lass probability factors for biofilm cultures that were e quivalent to those previously found for suspended cultures. The probab ility of plasmid loss in the B, cepacia 17616-TOM31c biofilm cultures was equivalent to those found in the suspended cultures. The results i ndicate that biofilm growth neither helps nor hinders plasmid stabilit y. In both the suspended and the biofilm cultures, plasmid retention a nd expression could be maintained using selective growth substrates an d/or an appropriate plasmid-selective antibiotic. (C) 1998 John Wiley & Sons, Inc.