Biofilm formation by the yeast Rhodotorula mucilaginosa: process, repeatability and cell attachment in a continuous biofilm reactor

Abstract

Yeast biofilms contribute to quality impairment of industrial processes and also play an important role in clinical infections. Little is known about biofilm formation and their treatment. The aim of this study was to establish a multi-layer yeast biofilm model using a modified 3.7 l bench-top bioreactor operated in continuous mode (D = 0.12 h⁻¹). The repeatability of biofilm formation was tested by comparing five bioprocesses with Rhodotorula mucilaginosa, a strain isolated from washing machines. The amount of biofilm formed after 6 days post inoculation was 83 μg cm⁻² protein, 197 μg cm⁻² polysaccharide and 6.9 × 10⁶ CFU cm⁻² on smooth polypropylene surfaces. Roughening the surface doubled the amount of biofilm but also increased its spatial variability. Plasma modification of polypropylene significantly reduced the hydrophobicity but did not enhance cell attachment. The biofilm formed on polypropylene coupons could be used for sanitation studies.

Keywords:

• yeast
• Rhodotorula mucilaginosa
• model biofilm
• test system
• bioprocess

Acknowledgements

This work has been financially supported by the Swiss Commission for Technology and Innovation (CTI project 9075.1PFLS-LS). Special thanks go to Max Keller, Joerg Gschwend, and the whole team of Empa's machine shop for the construction of the cylinder for the biofilm reactor. The authors also thank Kathrin Grieder, Aline Hunziker, Bettina Lanz and Monika Braegger for the microbiological analysis, Barbara Hanselmann for the plasma treatments, Patrick Rupper for XPS analyses, Miele and Treff AG for providing polypropylene material, and Bruno Wampfler for fruitful discussions about the manuscript.