(188de) Computational Modeling of Biofilm Chemotaxis Induced By a Carbon-Rich Plume in Sediments

After an oil spill in the sea, part of the crude oil ends up in the form of droplets trapped between the grains of a sandy shoreline, or the sediments of the seafloor. For example, in surface oil spills, tidal pumping promotes the infiltration of oil into the sand when the oil slick reaches at a seashore. Moreover, in deep sea oil releases, dispersed oil droplets aggregate with marine snow and settle down on the seafloor. In all these cases, the dissolution and primary degradation of the trapped or deposited oil create a carbon-rich plume that disperses deeper into the granular pore structure and triggers chemotactic responses of indigenous oil-consuming microbial species. Swarms of individual chemotactic microbes swim within the pore space or crawl over the pore surface and are followed by slowly advancing biofilm communities.

In particular, the migration of a biofilm as a whole towards a nutrient source is called biofilm chemotaxis and occurs even if the individual microbes that compose the biofilm are neither chemotactic nor motile. This interesting phenomenon is caused by anisotropic growth with higher rates of cell proliferation and extracellular matrix synthesis along the nutrient concentration gradient. Fluid flow tends to suppress biofilm chemotaxis through metastatic events that involve the downstream relocation of biofilms via creep or detachment. Under certain conditions, biofilms have been experimentally observed to overcome fluid stresses and migrate against the direction of flow in porous media. Yet, the pertinent theoretical analysis has not received the deserved attention.

This work presents a computational demonstration of upstream biofilm migration that is driven by a carbon-rich nutrient supply within a sedimentary porous medium. The process is analyzed at the pore scale with a hybrid computer simulator that combines continuum-based descriptions of fluid flow and solute transport with particle-based descriptions of biofilm growth and detachment (Kapellos et al., 2015). Specifically, the Navier-Stokes-Brinkman equations, poroelasticity equations, and convection-diffusion-reaction equations are solved numerically for the determination of the fluid velocity, biofilm stress, and solute concentration fields. Biofilm growth is described with an on-lattice cellular dynamics model and biofilm metastasis is described with a three-step (crack-roll-flow), on/off-lattice particle transport model. It has been found that biofilms propagate through the pore space and towards the nutrient source as a reactive wave leaving behind oxygen depleted regions filled with inert biomass of apoptotic cells and residual extracellular matrix (Kapellos, 2018).

Acknowledgements: This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 741799 (project "OILY MICROCOSM").

References:

Kapellos, G.E. "Computer simulation of upstream biofilm migration in sediments", Frontiers in Environmental Science, under review (2018).

Kapellos, G.E., Alexiou, T.S. and Pavlou, S. "Fluid-biofilm interactions in porous media", In: Becker, S.M. and Kuznetsov, A.V. (Eds.), Modeling of Microscale Transport in Biological Processes, Elsevier, 207-238 (2015).