Hydrodynamic Effects on Biofilms at the Biointerface Using a Microfluidic Electrochemical Cell: Case Study of Pseudomonas sp.

Abstract

The anchoring biofilm layer is expected to exhibit a different response to environmental stresses than for portions in the bulk, due to the protection from other strata and the proximity to the attachment surface. The effect of hydrodynamic stress on surface-adhered biofilm layers was tested using a specially designed microfluidic bio flow cell with an embedded three-electrode detection system. In situ electrochemical impedance spectroscopy (EIS) measurements of biocapacitance and bioresistance of Pseudomonas sp. biofilms were conducted during the growth phase and under different shear flow conditions with verification by other surface sensitive techniques. Distinct, but reversible changes to the amount of biofilm and its structure at the attachment surface were observed during the application of elevated shear stress. In contrast, regular microscopy revealed permanent distortion to the biofilm bulk, in the form of streamers and ripples. Following the application of extreme shear stresses, complete removal of significant portions of biofilm outer layers occurred, but this did not change the measured quantity of biofilm at the electrode attachment surface. The structure of the remaining biofilm, however, appeared to be modified and susceptible to further changes following application of shear stress directly to the unprotected biofilm layers at the attachment surface.

Flow‐Based Deacidification of Geobacter sulfurreducens Biofilms Depends on Nutrient Conditions: a Microfluidic Bioelectrochemical Study

“…Byproducts from half‐cell reactions at the WE and the counter electrode (CE) were carried downstream and did not contaminate the liquid environment around the RE because the upstream diffusion of H + was slower than the downstream convection (see Table S1 for mass transfer calculation results). The electrode configuration which placed the RE upstream were it could be exposed to a constant flux of fresh nutrient media has been shown previously as a method for achieving stable performance from an Au pseudo RE for non‐electroactive bacteria and their biofilms ,. For electroactive biofilms used here, stability was enhanced because G. sulfurreducens bacteria could not complete the Krebs cycles via electrode respiration at the RE because no current is permitted to flow through it.…”

“…To better understand how the bulk flow of a typical Ac‐based nutrient solution affects the pH b of a G. sulfurreducens biofilm, a three‐electrode microfluidic system was used. The reader is directed to previous work that discusses the fabrication protocol to insert the electrodes flush against the microchannel wall in a similar device used for electrochemical impedance spectroscopy of non‐electroactive biofilms . Figure a shows the device schematic, including placement of electrodes and direction of liquid flow.…”

“…The reader is directed to previous work that discusses the fabrication protocol to insert the electrodes flush against the microchannel wall in a similar device used for electrochemical impedance spectroscopy of non-electroactive biofilms. [29] Figure 1a shows the device schematic, including placement of electrodes and direction of liquid flow. Figure 1b shows an electron microscopy image of the orientation of a mature biofilm on the WE following an experiment.…”

A Generalized Kinetic Framework Applied to Whole‐Cell Bioelectrocatalysis in Bioflow Reactors Clarifies Performance Enhancements for Geobacter Sulfurreducens Biofilms

“…The channel-embedded electrodes were fabricated as shown previously. [26,30] Graphite was used for both the working (WE) and counter (CE) electrodes and a stable gold (Au) pseudo reference electrode (RE). The device was operated in an anaerobic enclosure with controlled temperature of 23 � 0.5°C.…”

“…Frozen samples of Geobacter sulfurreducens (strain PCA, ATCC 51573), were cultured under controlled temperature and deoxygenated conditions before being injected into the microfluidic electrochemical device. The channel‐embedded electrodes were fabricated as shown previously ,. Graphite was used for both the working (WE) and counter (CE) electrodes and a stable gold (Au) pseudo reference electrode (RE).…”