Diffusiophoretic Bioaugmentation: Boosting the Bacterial Motility in Soil Matrix by Chemical Gradients for Enhanced Bioremediation

When a toxic chemical spill occurs, the chemicals often leak into the soil, making it difficult to remove because the chemicals can easily seep deep underground. To clean up the spill, chemical-degrading bacteria can be injected into the contaminated soil. One of the major challenges of this approach is delivering the bacteria directly to the contaminated site. If the chemicals are deep in the soil, the injected bacteria must sense and swim towards the contaminants which can be a slow process. The goal of this project is to speed up the movement of the bacteria toward the contaminated site by injecting the bacteria into the ground with additional non-toxic chemicals that can enhance their motion by creating chemical gradients. Successful completion of this project will benefit society by developing environmental remediation strategies to mitigate ecological and human health impacts of toxic pollutants. Additional benefits to society will be accomplished through student education and training including the mentoring of a graduate student at the University at Buffalo. Toxic chemical spills require processes to degrade the chemicals to avoid environmental and human health impacts. Successful bioremediation of chemical spills requires directing decomposer bacteria to the target soil micropores that are deep in the subsurface where contaminants are likely to persist. The small bacteria can passively advect across permeable regions of the subsurface via pore flow. However, impervious micropores, which are prevalent in the soil matrix, can only be accessed by active motility or Brownian motion. These areas often tend to hold a significant amount of contaminants since they cannot be easily swept away by the pore flow, thus limiting the remediation efficacy. Therefore, there is a critical need to develop an effective way to disperse bacteria to hard-to reach spaces. The main objective of this proposal is to achieve enhanced bioremediation by introducing chemical heterogeneity in the soil. The central hypothesis is that the chemical gradients created within the soil matrix during bioremediation can accelerate the bacterial transport not only by chemotaxis, the movement by intracellular transduction of an organism in response to chemical stimulus, but also by diffusiophoresis, the directed migration of colloidal particles along chemical gradients due to the physicochemical interactions between the surrounding chemicals and the particle surface. When the chemical and cell surface conditions are met, diffusiophoresis can enhance the transport of bacteria by orders of magnitude compared to Brownian motion regardless of the bacteria type. This investigation will include experimental characterization of the interplay between chemotaxis and diffusiophoresis in microfluidic systems and laboratory-scale bioremediation demonstration in the soil matrix. This research aims to elucidate the fundamental aspects of bacterial diffusiophoresis and demonstrate an effective, low-cost strategy to enhance bioremediation . Further societal benefits include introducing undergraduate engineering students to microbial engineering through a hands-on course that will be developed to include various aspects from cell culture and microfluidic fabrication to laboratory-scale bioremediation as well as mentoring of a graduate student. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.