Pore-scale origin of flow-induced bio-aggregate formation
Abstract
Microbes in natural and engineering systems are often found as aggregates consisting of microbial communities, organic and inorganic matters and water. Such bio-aggregates play an important role in shaping biogeochemistry of soil and groundwater environments, in clogging of porous media, biofilm formation, and human lung infections (Baveye & Darnault, 2017; Ebrahimi & Or, 2016; Trunk, S. Khalil, & C. Leo, 2018). In addition, aggregation offers microbes enhanced protections against external stresses and helps them coping with environmental changes.
Studies have reported that microbes autoaggregate through intercellular adhesion induced by homolytic interaction between autoagglutinins. While bio-aggregate are often generated in porous systems, the role of pore-scale flow and porous media structure on aggregation is poorly understood. In this study, we combine microfluidics experiments and numerical simulations to demonstrate that the unique flow structure at constriction points of the pore-throats, which is ubiquitous in porous media, induces bio-aggregate formation. A single channel with sinusoidal pore-throat was used as a porous media analog system (FIG. 1A). Upon injection of an E. coli suspension (OD600 = 0.1) at a constant flow rate (0.2 μl/min), we observed the formation of bio-aggregates at the pore-throat while on the straight walls only attachment and growth were detected (FIG. 1B - D). Once a large cell aggregate is formed, the biomass is flushed downstream due to the clogging and the resulting pressure build-up at constant flow rate. A series of subsequent experiments revealed that the combination of streamline focusing and secondary flow facilitates attachment and capture of cells at the pore-throat, inducing aggregation. In addition, through experiments and numerical simulation in a broad range of flow rates, we identified a critical shear stress value (~ 2 Pa) below which an aggregate forms and above which biofilm streamer forms. We further show that such flow-induced aggregation occurs in diverse geometries of throats and different strains of E. coli. This study elucidates the pore-scale origin of bio-aggregate and streamer formation. References Baveye, & Darnault (2017). PNAS. 114(14) Ebrahimi, & Or (2016). Glob. Change Biol., 22(9)- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH023...09L
- Keywords:
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- 0412 Biogeochemical kinetics and reaction modeling;
- BIOGEOSCIENCES;
- 0448 Geomicrobiology;
- BIOGEOSCIENCES;
- 1813 Eco-hydrology;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY