Antibiotic resistance genes (ARG) are an increasing threat to the economy and health care [1]. Wastewater treatment systems are widely considered hotspots for their dissemination into the environment, possibly leading to the enrichment of the environmental resistome by horizontal gene transfer or by selection pressure. Membrane bioreactors (MBR) can reduce organic load and remove partly ARGs. Physical-chemical membrane properties (pore size distribution, hydrophobicity, and surface roughness) and fouling (organic and inorganic) are considered to contribute to the removal capacity either by sorption or degradation. Underlying processes and counter-influences on transport mechanisms are not yet fully understood. Biotic fouling layers can lower membrane performance by reducing permeation and provide for possible degradation or sorption, leading to higher ARG retention. Increasing shear stress is expected to lead to higher biofilm density, thus lowering permeation and transport processes.

Experimental setup
A fully automated fouling simulator platform, consisting of an XYZ-manipulator (Minimill XL Pro, QBOT) steering an optical coherence tomography (OCT) (ThorLabs) measurement head at defined positions over 18 stirrer cells will be running at different operational conditions. Automation will be executed from a Raspberry Pi using Python for emulation of G-Code addressing the manipulator and controlling the OCT. The cylindrical stirred cell reactors will be operated dead end and grouped in packs of 6 stirrers (IKA TWISTER) each pack operated in slave mode. Computational Fluid Dynamics will enable estimation of the induced shear force on the membrane surface, i.e., fouling layer. In the following, simulations will enable (figuring out) possible mechanisms and processes underlying changes in mass transfer coefficients or transport of free DNA. Biomolecular analysis of the permeate will allow for efficient approximation of ARG retention. In combination with shear stress approximation by CFD, the rupture likeliness of plasmids can be related.

Aim
Uptake and degradation of free DNA (represented by genetically modified plasmids) can be increased by optimization of operational parameters, e.g., shear rate. Understanding of underlying processes influencing the mass transfer of free DNA enables improvement of operational conditions or setups of MBRs achieving higher retention rates of free DNA by controlling fouling layer development.

References

[1] ECDC, Final report - Subgroup established under the EU AMR One Health Network to formulate suggestions for AMR Actions - European Commission, Directorate-General for Health and Food Safety, 2022.