Anaerobic soil-pores and sediments are strongly heterogeneous at the microscopic scale, creating a diverse and complexly distributed array of stress promoting chemical and physical microenvironments that may be advantageous for accelerated microbial adaptation and evolution. A microfluidic platform was fabricated (i.e. microfluidic gradient cell, MGC) to explore how microorganisms interact with the environment and regulate their response to spatial gradients of stressors. The MGC’s design contains two boundary channels on either side of an interconnected matrix of hexagonal wells. The MGC allows to precisely manipulate chemical inputs, mimic microbe natural microenvironments, and perform real-time in-vitro analysis of cell location, shape, and motility via time-lapse imaging on a Nikon Eclipse Ti-E system. Shewanella oneidensis MR-1 is highly motile, and chemotactic driven motility allows cells to migrate and thrive in highly toxic environments when other chemo-attractants (i.e., nitrate, lactate) are present. S. oneidensis MR-1 was subjected gradients of sub-lethal and lethal ciprofloxacin boundary concentrations. Remarkably, in conditions up to 250x MIC, an increase in cell density was observed over time. In addition, effluent collected from ciprofloxacin boundary channel indicates that the cells were metabolically active. To further test this hypothesis, experiments were conducted with mutant S. oneidensis MR-1 (e.g., dflaAB, dmotAB, dpomAB, and dmotpomAB) strain that impede motility. Overall, these studies suggest that chemotaxis driven motility play a large role in the habitability of toxic environments if a flux of nutrient-rich compounds is present. Beyond the underlying mechanism of resistance, group-level traits such as chemotactic motility provide a competitive advantage that can allow for better prediction of microbial diversity, adaptation, and evolution.

Physiological response of Shewanella oneidensis MR-1 to spatial gradients of ciprofloxacin concentration

255th National Meeting (2018)

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