es8b04838_si_001.pdf (6.9 MB)
Motility of Shewanella oneidensis MR‑1 Allows for Nitrate Reduction in the Toxic Region of a Ciprofloxacin Concentration Gradient in a Microfluidic Reactor
journal contribution
posted on 2019-01-23, 00:00 authored by Reinaldo
E. Alcalde, Kyle Michelson, Lang Zhou, Emily V. Schmitz, Jinzi Deng, Robert A. Sanford, Bruce W. Fouke, Charles J. WerthSubsurface
environments often contain mixtures of contaminants
in which the microbial degradation of one pollutant may be inhibited
by the toxicity of another. Agricultural settings exemplify these
complex environments, where antimicrobial leachates may inhibit nitrate
bioreduction, and are the motivation to address this fundamental ecological
response. In this study, a microfluidic reactor was fabricated to
create diffusion-controlled concentration gradients of nitrate and
ciprofloxacin under anoxic conditions in order to evaluate the ability
of Shewanella oneidenisis MR-1 to reduce the former
in the presence of the latter. Results show a surprising ecological
response, where swimming motility allow S. oneidensis MR-1 to accumulate and maintain metabolic activity for nitrate reduction
in regions with toxic ciprofloxacin concentrations (i.e., 50×
minimum inhibitory concentration, MIC), despite the lack of observed
antibiotic resistance. Controls with limited nutrient flux and a nonmotile
mutant (Δflag) show that cells cannot colonize
antibiotic rich microenvironments, and this results in minimal metabolic
activity for nitrate reduction. These results demonstrate that under
anoxic, nitrate-reducing conditions, motility can control microbial
habitability and metabolic activity in spatially heterogeneous toxic
environments.