In situ effective diffusion coefficient profiles in live biofilms using pulsed‐field gradient nuclear magnetic resonance

Abstract

Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well-documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: 1) invasive to the biofilm, 2) performed under unnatural conditions, 3) lethal to cells, and/or 4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time-dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: 1) measure the effective diffusion coefficient for water in live biofilms, 2) monitor how the effective diffusion coefficient changes over time under growth conditions, and 3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1 biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (Drs) profiles. We found that 1) Drs decreased from the top of the biofilm to the bottom, 2) Drs profiles differed for biofilms of different ages, 3) Drs profiles changed over time and generally decreased with time, 4) all the biofilms showed very similar Drs profiles near the top of the biofilm, and 5) the Drs profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm.

Modeling Substrate Utilization, Metabolite Production, and Uranium Immobilization in Shewanella oneidensis Biofilms

“…Growing S. oneidensis Biofilms S. oneidensis MR-1 biofilms were grown using a constant depth film fermenter (CDFF) and then transferred to a specially designed NMR biofilm reactor to allow the biofilms to continue to grow inside the NMR biofilm reactor (Figure 2), as described in a previous study (Renslow et al, 2010). Briefly, the biofilms were grown aerobically at 30 • C on 5 mm-diameter glass coverslips in the CDFF wells.…”

“…Laminar flow with no-slip conditions is justified because of the low Reynold's number (0.1) in the NMR biofilm reactor (Renslow et al, 2010). The far upfield boundary is the outlet.…”

“…The development of an integrated model has been hindered by the limitations of the experimental techniques required to investigate biofilms and collect necessary experimental data, such as maximum specific growth rates, half saturation constants, cell yields, stoichiometric coefficients, and effective diffusion coefficients. Recently, we developed a nuclear magnetic resonance (NMR) microimaging-capable biofilm reactor which can be used for in situ monitoring of live biofilm metabolism and U immobilization, which allows us to generate these critically needed data (Mclean et al, 2008a,b;Renslow et al, 2010Renslow et al, , 2014Renslow R. S. et al, 2013). Recently, FIGURE 1 | U(VI) immobilization through reductive (direct and indirect reduction) and nonreductive (i.e., biosorption, bioprecipitation, and bioaccumulation) mechanisms of bacteria.…”

Mass transfer in a membrane aerated biofilm

“…Beyenal et al (1998) utilisent des microsondes pour mesurer la diffusivité relative du ferricyanide de potassium. Mais le ferricyanide a pour propriétés de désactiver les biofilms et donc de modifier son comportement (Renslow et al, 2010). De plus, le transfert de matière dans un biofilm étant un mélange de convection et de diffusion (De Beer et Stoodley, 1995), une couche limite diffusionnelle peut se former autour de la microsonde (Coeuret et Stork, 1993) qui, si elle n'est pas prise en compte dans le calcul de la diffusivité relative, risque de conduire à sous-estimer la mesure.…”

“…De plus, le transfert de matière dans un biofilm étant un mélange de convection et de diffusion (De Beer et Stoodley, 1995), une couche limite diffusionnelle peut se former autour de la microsonde (Coeuret et Stork, 1993) qui, si elle n'est pas prise en compte dans le calcul de la diffusivité relative, risque de conduire à sous-estimer la mesure. Renslow et al (2010) rapportent également la limite à l'utilisation des microsondes à la base du biofilm, à cause des limites du transfert autour de la tête de microsonde quand elle est proche de la surface solide.…”