Alex Tam (The University of Queensland, School of Mathematics and Physics)

Approximately 80% of microbial life exists in biofilm colonies, consisting of cells embedded in an extracellular fluid matrix. Biofilms of pathogenic yeast species can colonise indwelling medical devices, making them a leading cause of hospital-acquired infections. Since biofilms are highly resistant to anti-microbial treatment, the mortality rate of these infections can approach 40% for patients in intensive care units. With the objective of better understanding and controlling growth, experimentalists have developed methods to initiate yeast biofilm formation in controlled laboratory environments. In these experiments, biofilms expand radially at an approximately constant speed, and adopt a non-uniform floral pattern consisting of petal-like structures. However, the physical mechanisms underlying this growth remain unknown.

We investigate two hypothesised mechanisms of yeast biofilm expansion. First, we use a reaction--diffusion system with a nonlinear, degenerate diffusion term for cell spread to investigate the hypothesis that biofilms expand by nutrient-limited growth. Using travelling wave and linear stability analysis, we show that the model can explain the approximately constant expansion speed, and predict the petal formation observed in experiments. Second, we consider a more detailed two-phase, thin-film model that incorporates nutrient uptake and the mechanics of extracellular fluid flow in addition to nutrient limitation. We find good agreement between numerical solutions to this model and experimental data for realistic parameter values. From this, we conclude that sliding motility, which describes expansion driven by cell proliferation and weak adhesion to the substratum, is a possible mechanism for biofilm growth.

About Applied and computational maths seminars

Our seminars bring together UQ's applied and computational mathematics communities.

UQ and invited scientists deliver the presentations, which are informal and promote discussion.

We welcome suggestions for speakers and topics from staff, students and visitors, and encourage students to share their work.

Our seminars are usually held on Thursdays from 3pm to 4pm.

To suggest a topic or speaker, and for more information, contact Dr Dietmar Oelz or Dr Fred Roosta-Khoransani.


Physics Annexe (06)