Biofilm thickness matters

Does biofilm thickness matters?

Biofilms are agglomerations of microbial cells attached to each other or to surfaces (like the slime on river rocks or the slimy, sticky goo in bathrooms). Their thickness can vary, and that thickness can be influenced by many factors. For example, older biofilms would be thicker than newer ones. Nutrient availability can also result in bigger biofilms. Other factors like microbial predation, water flow and turbulence may also limit biofilm thickness.

Intuitively, we would think that the tickness of a biofilm matters. A thicker biofilm would have more cells. It could also have a more heterogenous structure. In thick biofilm the cells in the interior may have limited access to nutrients, and even lack access to oxygen, which would influence their metabolism. But the importance of biofilm thickness itself had never been studied, as it is often linked to other parameters, like biofilm age.

We answered this question in two scientific publications: One at Water Research, and another at Scientific Reports. In the two studies we controlled the thickness of a biofilm, to 50 and 400 micrometres, and we kept all the other conditions the same, by keeping both thin and thick biofilms in the same nitrifying bioreactor.

Picture of thick (above) and thin biofilms (below). Scale bar: 100 micrometres.

We discovered that thick and thin biofilms not only look different, but they also behave different, and differ in their microbial community composition. For example, we observed anammox bacteria in thick biofilm, but they were absent in thin biofilms. This was probably due to thin biofilms being fully oxygenated, which would inhibit the growth of anammox bacteria, as these bacteria are sensitive to oxygen.

Biofilms are ubiquitous in nature and engineered environments, and thus these results are not only important for biofilm researchers, but also for people working in wastewater treament, drinking water treatment, medical microbiology environmental microbiology and biofouling.

Read more about biofilm thickness:

Suarez, C., Piculell, M., Modin, O. et al. Thickness determines microbial community structure and function in nitrifying biofilms via deterministic assemblySci Rep 9, 5110 (2019).

Piculell, M. et al. The inhibitory effects of reject water on nitrifying populations grown at different biofilm thicknessWater Res. 104, 292–302 (2016).

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