ADAPTATION OF ESCHERICHIA COLI TO CIPROFLOXACIN GRADIENTS IN A POROUS MICROFLUIDIC DEVICE

Microorganisms are an influential component of many common sedimentary systems. Gradients in temperature and pH, substrate availability and spatial and temporal fluctuation of aqueous chemistry in these environments drive microbial evolution and adaptation in these systems. Next-generation microfluidic devices now permit previously unattainable levels of control and reproducibility of these dynamic chemical environmental stresses. They also provide a consistently reliable real-time means to quantitatively track microbe abundance along a stress gradient. In the present study, newly designed and fabricated microfluidic devices with porous media have been utilized to determine the chemical stress fields that enhance the rate of adaptation and thus to test how E. coli bacterial communities adapt to antibiotic stresses. By applying antibiotic and nutrient into inlet channels adjacent to either side of the porous media inoculated with E. coli, a gradient of antibiotic was formed. Hydrogel barriers were selectively photo-polymerized in between of the inlet channels and the porous media to prevent any undesired convection. Hence, chemical solute can only be transported through the hydrogel by diffusion, creating a reproducible antibiotic gradient over the porous media. The bacteria were also constrained by the hydrogel boundary barriers from escaping the porous media. Preliminary observations suggest that the number of E. coli cells increased over time in regions with lower ciprofloxacin concentration. In regions with higher antibiotic concentrations, cell number initially decreased and then fluctuated. The overall distribution of E. coli biomass in the porous media showed good correlation with the linear gradient of stress and nutrients at steady state. The area with the most abundant bacteria is the most optimal environment in the system and might indicate the microchemical conditions which enhance survival and evolution. Future work will evaluate effects of other environmental stresses, including pH, oxygen availability on microorganisms adaptation in sedimentary systems.