טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLaout Natalia
SubjectThe Influence of Electrochemical Polarization on Bacterial
Adhesion to Different Metals
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Avi Ostfeld
Professor Robert Armon


Abstract

The development of biocide free ecological counter-measures against biofouling requires basic research of various factors that affects primary steps of microbial adhesion. The present study was aimed to assess the effect of electrochemical polarization on the early stages of bacterial adhesion onto metallic substrata. Among the parameters studied were: medium chemical composition, bacterial hydrophobicity/hydrophilicity and metal nature. Investigations were carried out on an especially designed electrochemical set-up allowing to study bacterial adsorption onto metals in a wide potential region [-0.8 to +1.1 V (SCE)] in one experiment. Adsorption of experimental Flavobacterium breve, Pseudomonas fluorescens P17, iron bacteria and heterotrophic aerobic bacteria isolated from tape water (mixed culture) to platinum, titanium, stainless steel, aluminum alloy, and cooper was investigated. A well-defined peak characterized bacterial adsorption dependence on externally applied potential. Maximum adhesion for all experimental substrates occurred in the potential range of -0.3 to +0.5 V (SCE). Shift of applied potential toward both positive and negative direction from this maximal adhesion potential was associated with a gradual reduction in bacterial adhesion. The extent of bacterial adhesion strongly depended on the bacterial nature and on metallic substratum. Initial microbial adhesion was strongly influenced by ionic strength of the suspension solution. Bacterial adhesion was also affected by cationic or anionic composition of suspending medium. Adhesion of tested bacteria was efficiently reduced by addition to experimental medium of the non-ionic surfactant Tween 80 or bovine serum albumin.  In order to explain the polarization effect on bacterial adhesion onto metallic surfaces a process model was applied and discussed.