The transfer of genetic information in the environment has been an important issue among scientists and the public for several decades. Its importance first became apparent with the rapid spread of antibiotic resistance to pathogenic bacteria. Then genomic analysis revealed that gene transfer has played an important role in bacterial evolution. Recently there have been public concerns about risks associated with gene transfer from genetically engineered organisms to indigenous organisms and the possible consequences in the environment. Cell to cell transfer is one of the primary means by which genes can be propagated in natural geologic formations into alternate hosts. Although the process has been documented and exchange occurs under laboratory conditions, very little is known about the frequency of these events in the subsurface. The natural geologic environment is heterogeneous, and therefore it has been impossible to test every variable experimentally over a hierarchy of scales. By combining experiment with theory the investigators target identification of the major requirements for successful gene transfer and the rates at which it occurs under particular conditions. The transfer of genetic material among bacteria in the environment can occur both in the planktonic and attached state. This study focuses on the development and application of mathematics to describe the fundamental aspects associated with horizontal gene transfer within biofilms in the subsurface. The mathematics used to describe bacterial transport in porous media has been focused on colloid transport mechanisms for single cell or cell clump transport. These two fields are so far in nearly complete isolation from each other. Here the investigators propose experiments and modeling designed to test hypotheses regarding transfer in porous media at multiple scales, and to elucidate priority mechanisms controlling transfer among bacteria undergoing transport, attachment, and biofilm formation.
