Influence of surface properties on adhesion of Cobetia marina and accumulation of marine microfoulers in the ocean

Abstract

Marine biofouling, the colonization of submerged surfaces by unwanted organisms, has an important economic and environmental impact. This PhD thesis focuses on the smaller organisms involved in the biofouling process such as bacteria, diatoms and protozoa also called microfoulers. As bacteria are usually among the first organisms to settle on submerged surfaces, the characterization of their adhesion to these surfaces is essential for the development of strategies for antifouling, and in particular fouling release coatings. To this end, the adhesion of the bacterium Cobetia marina on various model systems for anti fouling coatings was investigated using a microfluidic shear stress assay which applies shear stresses covering a range of nearly six orders of magnitude from 0.01 to 5,500 dyn/cm2. For this assay, the experimental parameters such as medium, incubation time and increase of the applied volumetric flow were optimized. In this work various surface properties relevant for bioadhesion were investigated, namely wettability, chemistry, hydration, transition from monolayers to polymeric coatings, and the controlled release properties of metal organic frameworks as a smart release coating. The surfaces used for this study were self-assembled monolayers (SAMs) with different chemical end groups and hydration levels, polysaccharide coatings with and without capping of their carboxylic groups, poly[oligo(ethylene glycol)methacrylate] (POEGMA) brushes and copper based metal organic frameworks (Cu SURMOF 2). The results showed that in general the hydration of the surface is more important for the resistance against bioadhesion than the wettability. It was demonstrated that the critical shear stress needed for removal of bacteria from a SAM system based on ethylene glycols (EGs) decreased with an increasing number of EG units which is directly related to an increment of hydration. Furthermore, good fouling release properties of polysaccharide coatings were demonstrated, especially if the free carboxyl groups of alginic acid (AA) and hyaluronic acid (HA) were capped with a hydrophobic amine. Cu SURMOFs 2 were investigated as an example of smart release coatings. When bacteria interacted with these surfaces they induced a loss of crystallinity and a harmful effect on themselves. These findings, together with the observed stability of the coatings in artificial seawater (ASW) and the integrity of the coating in areas without bacteria demonstrated a stimulus response of these surfaces upon presence of bacteria. In order to compare the performance in the field of the surfaces investigated in the laboratory assays, a set of well characterized samples were immersed into the ocean at the Sebastian test site of the Florida Institute of Technology. The aim of these field tests was to compare the results of the laboratory experiments, which solely investigated a single species under controlled conditions, with field experiments which employed a mixed species marine environment under natural conditions. The results showed that air and water temperature seemed to be an important factor for the abundance of species and composition of the fouling community. Furthermore, the level of hydration of the surfaces was found to be more important for their colonization than their wettability. Some trends that have also been observed in previous laboratory assays such as the good performance of the polysaccharide coatings and the EG SAMs, compared to other SAMs, could be confirmed in the field. Hence, the inert properties of hydrophilic hydrogels could be demonstrated in both laboratory assays and in the natural marine environment.