EPS and water in biofilms

Planktonic life is dangerous for most bacterial strains and adhesion to surfaces is often considered a survival mechanism. Once adhering, the production of an extracellular matrix leads to the formation of what is generally called a “biofilm”. Biofilms grow on almost every surface to cause various clinical, industrial and environmental problems. Complete killing or removal of biofilms is difficult because bacteria protect themselves in a biofilm mode of growth within a self-produced matrix that is composed of extracellular polymeric substances (EPS) and water. Therefore, this thesis aims to study the fundamental mechanisms of biofilm resistance to physical stress and the role of EPS and water. ATR-FTIR spectroscopy combined with tribometry indicated that the polysaccharide production per bacterium in the initial adhering layer was higher during growth at high shear than at low shear and this increased EPS production extended to entire biofilms, as indicated by tribometrically measured coefficients of friction (CoF). Biofilms grown under low shear however, were stimulated during tribometry to produce EPS, also after stress relieve. We developed a Optical Coherence Tomography (OCT) image analysis method to quantitatively relate whiteness intensities across biofilms with volumetric bacterial densities in biofilms. Transport and storage of water in channels and pores in a biofilm matrix are vital for biofilm survival. We propose a minimal channel width of three times the Debye-Huckel length to prevent electrostatic interactions of particles or molecules to be transported with the channel shores and a channel width to length ratio smaller than 0.3 to differentiate with pores.