Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Chemical and Biochemical Engineering


Rehmann, Lars


The control of biofilm formation is a major concern for industrial, environmental, and public health. Undesirable biofilms can harbor different disease-causing pathogens and shorten the operational life of different equipment. On the other hand, beneficial biofilms are also used in various applications and managing its growth and activity can be desirable. Killing the biofilm does not usually incorporate the removal of the dead biofilm structure that is adhered to the surface. Therefore, the aim of this thesis is to control biofilm formation; to be able to remove, inhibit, and enhance biofilm formation. This thesis investigated the use of norspermidine, D-amino acids, and selected enzymes for the control of biofilm formation. Biofilm was pre-grown in 96-well microtiter plates and the different treatments were applied for 24 h. Biofilm formation was quantified before and after treatments using crystal violet stain. The results obtained in this thesis showed that norspermidine had a dual effect on biofilms formation. A concentration of 1 mM norspermidine removed 39% of nonactive biofilm, while for active biofilm norspermidine enhanced the biofilm growth by 73%. D-amino acids can inhibit biofilm growth at a low concentration of 5 µM. The two D-amino acids used in this study, D-tryptophan (15 mM) and D-tyrosine (20 µM), removed 28% and 31% of biofilm, respectively. No clear synergetic effects were noticed from mixed D-amino acids treatment. The enzymes Savinase and Pectinex showed the highest biofilm removal among the different tested industrial enzymes. Savinase removed 68% and 84% while Pectinex removed 74% and 55% of biofilm formed by Bacillus species and Pseudomonas fluorescens, respectively. The optimized enzymatic treatment containing both Savinase (19.6 and 23.7 U/mL) and Pectinase (63.8 and 48.8 U/mL) showed the highest biofilm removal for Bacillus sp. biofilm at pH 6 and P. fluorescens at pH 8.