Horizontal gene transfer among microorganisms is a critical process that impacts bacterial evolution over long time horizons as well as the spread of traits such as antibiotic resistance on short time scales. Recently there has been heightened public concern about the risk of gene transfer from genetically engineered organisms to indigenous organisms and its consequences. Many environmental microorganisms spend a large part of their viable life cycle in the porous medium of the natural subsurface, such as soils and aquifer materials. Because it is a natural filter for water the subsurface also provides a mixing zone for different strains of bacteria, that each partition between the aqueous and solid phases. Thus to understand the ramifications of horizontal gene transfer in the natural environment, it is important to study the interactions between different species as they undergo fate and transport in porous media. The primary goal of this project is to evaluate the kinetics of microbial attachment-detachment to porous media solid surfaces, and the coupled kinetics of horizontal gene transfer in porous media via conjugation. The green fluorescent protein (GFP) gene expression system will be used with known hosts and recipients originally isolated from soils to quantify rates of conjugative gene transfer in controlled micromodel experiments. The gene transfer is expected to be limited by the paired residence time of host and recipient cells together on solid surfaces, and so the distributions of these paired residence times and the distribution of gene transfer times will be compiled from the micromodel experiments. The model for these data will be crafted by combining a biased Levy motion with drift for the bacterial transport in the porous media, with an alpha-stable random variable for residence time attached to surfaces, with a non-Markovian reaction kinetic model for the gene transfer from host to recipient. The intellectual merit of this project arises from the coordinated collaboration of people with expertise in hydrology, microbiology, molecular biology, applied mathematics, and physics, to (1) adapt new tools in genetic analysis and microscopy to study microbial activity and gene exchange at a molecular level in micro flow chambers, and (2) use mathematics to extrapolate the findings to understand processes at higher scales in the subsurface. By combining experiment with theory we may be able to determine the major requirements for successful gene transfer. The broader impacts of this project arise from the wide applicability of the results to many areas including human health, disease propagation, medicine, contaminant remediation, and evolutionary biology. All of these phenomena involve the processes studied here, many in porous media (subsurface or biotic). Educationally the project provides the venue by which results from the collaborative study can be incorporated into the PI's undergraduate and graduate courses in microbiology, engineering, and mathematics. The PI's also have a solid record in involving minorities and women in research, via the MARC/AIM program at Purdue, and the Women In Engineering (nee' Women Engineering Link) program at UC Davis, and this habit will be continued in this project.
