Two PhD positions in Biophysics and rheology of bacterial biofilms

Organisation/Company ETH Zürich Research Field Biological sciences » Other Physics » Biophysics Physics » Other Researcher Profile First Stage Researcher (R1) Country Switzerland Final date to receive applications 18 Jan 2026 - 22:59 (UTC) Type of Contract Temporary Job Status Part-time Hours Per Week 38 Is the job funded through the EU Research Framework Programme? Not funded by a EU programme Is the Job related to staff position within a Research Infrastructure?

No

Two PhD positions in Biophysics and rheology of bacterial biofilms

The bio Matter Microfluidics Group of Dr Eleonora Secchi at ETH Zurich is seeking two PhD candidates. Our research focuses on uncovering the physicochemical mechanisms that control microbial surface colonisation and biofilm assembly, structure, and rheology. We use a broad spectrum of technologies in materials science, microbiology, and microfluidics, as well as advanced imaging techniques to address our questions. We are a highly interdisciplinary, international, and collaborative team of about 10 members, hosted within the chair of Prof.

Roman Stocker in the Institute of Environmental Engineering.

Project background

The two PhD positions are part of a recently funded SNSF project aimed at systematically investigating nonlinear biofilm rheology, with emphasis on the role of extracellular DNA (eDNA). Biofilms are a ubiquitous form of microbial life with important implications in medicine, industry, and the environment. They are responsible for persistent infections, antibiotic resistance and biofouling, leading to economic costs of billions of dollars annually and thousands of deaths.

Biofilms are microbial communities encased in a polymeric matrix that provides mechanical stability and protection from mechanical stresses through its viscoelastic properties. While the linear viscoelastic response under small deformations is well characterised and recognised as a virulence factor, the response to large deformations remains poorly understood. In particular, there is a lack of systematic investigation of the nonlinear regime, where externally applied loads can induce stress-hardening and stiffening of the biofilm matrix.

Recent findings from our group suggest that eDNA may play a central role in the stress-hardening of biofilms. We hypothesise that this behaviour arises from the entropic elasticity of the eDNA network, a mechanism well described in polymer physics but largely unexplored in living biofilms. This could enable both short- and long-term adaptation to flow fluctuations. While initial experiments are consistent with this hypothesis, further investigation is required to validate the underlying molecular mechanisms and to determine whether stress-hardening is specific to streamers or constitutes a broader feature of biofilm mechanical adaptation across different morphologies.

This project will test these hypotheses through a combination of structural, biochemical, and rheological analyses of the biofilms and mathematical modelling, with the potential to reveal fundamental principles of biofilm resilience.

• Experimentally investigate nonlinear rheology and stress-hardening in bacterial biofilms with different morphologies using custom microfluidic and rheometry platforms.
• Quantify the role of eDNA and its interactions with biofilm matrix components using mutant libraries, enzymatic/antibody assays, and controlled physicochemical conditions; assess incorporation of exogenous DNA into biofilms and its impact on morphology and mechanics.
• Develop and apply advanced fluorescence/confocal imaging approaches to resolve biofilm network structure and eDNA conformation in situ.
• Contribute to the development of a numerical predictive model of biofilm mechanics.
• Collaborate within an interdisciplinary team and with external partners; communicate results through publications and presentations.

The tasks include wet-lab experimentation, project management, numerical modeling and teaching duties.

Start date:

February 1st, 2026, or by agreement

Fully funded PhD position (approximately 4 years). Final admission to the doctoral programme follows a successful Aptitude…