Gene transfer in microbial biofilms

Quantification and prediction of gene transfer in natural environments is required for reliable assessment of risks associated with the transfer of recombinant DNA in genetically engineered microbial inocula, and for a greater understanding of the mechanisms controlling transfer of genetic material. Published models of gene transfer describe plasmid transfer in homogeneous, liquid culture systems and do not consider the effects of surface growth or biofilm formation, which will be important in the majority of natural environments. To address this issue, a mathematical model has been constructed which describes bacterial plasmid transfer during colonisation of solid substrata. The model considers growth, colony expansion and substrate utilisation and generates predictions regarding changes in the numbers of donor, recipient and transconjugant cells. The model demonstrates the interactions between colony expansion, donor and recipient inoculum sizes and initial nutrient concentration in determining the final number of transconjugants, and explains a number of features observed in experimental studies of plasmid transfer during growth on particulate material.