Context. Biofilm formation in drinking water distribution systems (DWDS), which leads to numerous operational problems, i.e. secondary water contamination, pipe degradation and increased flow resistance, is influenced by many factors. Among these, surface characteristics, and thus pipe materials, have a strong influence on microbial initial adhesion. Sphingomonas species, due to their resilience and adaptability [1], are commonly found in DWDS biofilms communities, and have been recognized as surface colonizers.
Gap. Surface parameters, such as wettability, charge, roughness or topography are essential in governing initial microbial attachment [2], however, their role in the adhesion of potential surface colonizers in DWDS has not yet been studied.
Aim. Providing insight into initial adhesion mechanisms and biofilm forming properties of Sphingomonas spp. on polymeric pipe surfaces.
Methods. Sphingomonas strains, Sph5 and Sph10, isolated from water treatment plant spiral wound membranes, were cultivated in 6-well plates in presence of polyvinyl chloride (PVC-U) and polyethylene (PE100) coupons with R2A medium for 24 h, after which the adhering bacteria and the liquid phase were analyzed. Coupons surface and strains properties were also characterized.
Findings. Significant differences in adhesion between two strains were observed. While Spinhogomonas Sph5 attached as single cells, Sph10 tended to rapidly co-aggregate and adhered in a form of clusters creating three-dimensional layers, which accelerated biofilm formation, but limited the experimental reproducibility. Surface roughness and topography were the most distinct parameters for the tested materials, with PE100 being relatively smooth and PVC-U, rough and full of cavities. The roughness and cavities provided increased surface area available for bacterial adhesion, but also sheltered them from shear stresses.
Utilization. Implementing carefully selected strains, especially the potential surface colonizers such as Sphingomonas, in studying the interactions between the pipe surface and bacteria can provide more consistent insight into surface-driven biofilm formation mechanisms in DWDS circumstances.
