BACTERIAL RESPONSE TO MICROFLUIDIC STRESS GRADIENTS

Environmental stress gradients are common in sedimentary systems and potentially serve as the key factor driving microbial evolution. Furthermore, knowledge of the importance of gradients and bacterial response to stresses are critical for understanding the nature, speed and likelihood of evolution and adaptation of microbial life. It is difficult, however, for batch culture experiments in vials- the most common method used in prior studies, to maintain concentration gradients. To address this challenge in geobiology, we employ microfluidics in our experiments to mimic sedimentary settings that contain steep gradients in environmental stresses. We use microfluidic gradient cells (MGC) that enable microorganisms to explore different concentrations of stressors, thus allowing them to develop in ecological niches that best fit their physiology, all within a wide distribution of different stress gradients in the MGC.

We use a well-known model organism, Escherichia coli, to assess the feasibility of using MGC to promote evolution and adaptation. Fluorescence experiments were conducted to better evaluate stress response of E. coli to the antibiotic Ciprofloxacin. In vitro time-lapse images within the micromodel reveal that there were a proportion of cells that were able to utilize available nutrients in an environment of high dissolved Ciprofloxacin concentration. Image analysis shows the landscape distribution of microbial culture growth within the MGC, and computational models are employed to fit the data. Ongoing genomic and transcriptomic analyses will be used to track and analyze mutations in response to each level of Ciprofloxacin concentration.