MOBILIZATION OF BROAD-HOST-RANGE PLASMID FROM PSEUDOMONAS-PUTIDA TO ESTABLISHED BIOFILM OF BACILLUS AZOTOFORMANS - I - EXPERIMENTS

A strain of Pseudomonas putida harboring plasmids RK2 and pDLB101 was exposed to a pure culture biofilm of Bacillus azotoformans grown in a rotating annular reactor under three different concentrations of the l imiting nutrient, succinate. Experimental results demonstrated that th e broad host range RSF1010 derivative pDLB101 was transferred to and e xpressed by B. azotoformans. At the lower concentrations, donor mediat ed plasmid transfer increased with increasing nutrient levels, but the highest nutrient concentration yielded the lowest rate of donor to re cipient plasmid transfer. For transconjugant initiated transfer, the r ate of transfer increased with increasing nutrient concentrations for all cases. At the lower nutrient concentrations, the frequency of plas mid transfer was higher between donors and recipients than between tra nsconjugants and recipients. The reverse was true at the highest succi nate concentration. The rates and frequencies of plasmid transfer by m obilization were compared to gene exchange by ret retransfer. The init ial rate of retrotransfer was slower than mobilization, but then incre ased dramatically. Retrotransfer produced a plasmid transfer frequency more than an order of magnitude higher than simple mobilization. (C) 1998 John Wiley & Sons, Inc.