Biofilm formation of Methanosarcina barkeri on different support materials: applications for anaerobic digestion

Biofilms are sessile microbial communities attached to a surface, and offer a multitude of benefits to various biotechnological applications, such as anaerobic digestion. Therefore, engineering systems to promote biofilm formation is becoming increasingly desirable in the biotechnology sector. This thesis aimed to promote biofilm formation from the robust model methanogen, Methanosarcina barkeri, onto polymer support materials as a strategy for optimising the anaerobic digestion of domestic wastewater in peri-urban areas. A first step in this direction was to understand the effect of the support material on the biofilm-forming capabilities of M. barkeri. Various techniques were used throughout this thesis to show that the choice of support material was an important environmental factor in triggering different physiological responses from M. barkeri during biofilm formation. DLVO modelling, surface characterisation and static adhesion assays revealed the important role of the physicochemical surface properties of M. barkeri and the six support materials for initial microbial adhesion. M. barkeri was shown to exhibit different abilities to attach to the support materials, with the type of material strongly influencing the extent of initial attachment. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential analysis and fluorescence microscopy suggested that significant modifications to the cell surface occurred in response to attachment to a favourable support material (PVC), with increased levels of cell surface polysaccharides detected in biofilms attached to PVC compared to PETG. Furthermore, microbial attachment to PVC caused a significant higher relative abundance of proteins involved in methanogenesis, metabolism, cell wall biogenesis and EPS production compared to biofilms attached to PETG. The results from this thesis suggest that M. barkeri showcases different physiological responses for biofilm formation depending on the support material. Therefore, the choice of support material is an important design parameter for retaining microbial biomass within AD reactors, and should be considered in future design frameworks for high rate anaerobic digestion.