Browsing by Author "Murray, Thomas Everitt Rautenbach"

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    Interaction between plastic particles and biofilms
    (Stellenbosch : Stellenbosch University, 2023-03) Murray, Thomas Everitt Rautenbach; Wolfaardt, Gideon M. ; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The problem with plastic waste is immense and has received much attention in the last 15 years. Plastics break down into smaller plastic particles over time, from degradation that occurs from various sources. The natural environment poses many forces, including physical, chemical, and biological, which quicken the rate of degradation of plastic. These plastic particles are able to move through the environment due to natural forces which have managed to spread them everywhere. Accumulation of plastic particles is thus thought to be a problem which has the potential to effect living organisms on a large scale. There is reason to believe that association with and ingestion of plastic particles may cause health risks due to the size of the particles and harmful chemicals which may interact with them in the environment. Bacteria are amongst the first organisms which will interact when it is introduced into the environment. The formation of biofilms on the plastic may follow and in aqueous environments, may take only hours. These biofilms are robust and will proliferate under harsh conditions that may accelerate the degradation of the plastic polymer backbone and result in the production of plastic particles. Some microorganisms have the ability to produce plastic degrading enzymes which will enhance this process. They can also change their microenvironment enough to make plastic degradation less efficient and greatly alter the fate of plastic particles. The surfaces of weathered plastic particles are conducive to biofilm growth and thus strong relationships exist with biofilms that form on plastic particles. Information is, however, sparce on the inverse relationship which plastic particles may have with biofilms. While plastic particles are common in the environment, biofilms are ubiquitous. There are thus many environments containing biofilms which may be greatly changed by the introduction of plastic particles. In the experimental section of this project a method was developed to study interactions between biofilms and plastic particles in a simulated continuous flow environment. The fluorescently labelled bacteria used in the study, in this case Pseudomonas fluorescens CT07::gfp were selected due to their affinity for growing as a biofilm. This is important as it facilitates a more realistic environment than a conventional planktonic culture would. The method was successful in detecting accumulation of plastic particles under specific conditions and measuring how the relationship of particle accumulation was affected by altering specific parameters of the system, like the concentration of plastic particles and nutrients in the growth medium. It was determined that biofilms cultured in lower nutrient medium concentration of tryptic soy broth (0.3 g/L) resulted in the adherence of significantly more plastic particles in the flowcells than the higher nutrient medium concentration (3.0 g/L). Furthermore, both biofilms resulted in the adherence of significantly more plastic particles in the flowcells than the sterile controls which were performed, and which had no significant difference between each other. The process of bead adhesion was observed and documented to be due to multiple factors, including extracellular polymeric substances (EPS), biofilm cells, and shear forces at the flowcell surface. It was determined that the presence of a biofilm resulted in significantly more plastic particles accumulating in the biofilm than the absence thereof, indicating that there is significant interaction between the biofilm and plastic particles. The binding ratio of each of the biofilms was calculated by determining the total theoretical number of adhered plastic particles in each flowcell and dividing that by the total number of plastic particles that had passed through each flowcell. A constant binding ratio was obtained for each biofilm cultured on the different nutrient medium concentrations which also remained constant when the concentration of plastic particles was changed Furthermore, the potential of biofilms as plastic particle traps was explored due to the observed relationships, but a low efficiency of bead binding was determined.