Surface adhesion of phototrophic biofilms

Cyanobacteria belong to the oldest known microorganisms and are capable of oxygenic photosynthesis. Depending on their habitat aquatic and terrestrial cyanobacteria are distinguished. Terrestrial cyanobacteria grow embedded in a matrix of extracellular polymeric substances (EPS) as phototrophic biofilms. Those EPS serve as nutrient storage, protection from desiccation and play an important role in surface adhesion. For cultivation of phototrophic biofilms different biofilm reactors have been developed in the last years. One interesting parameter when cultivating biofilms is the surface material and structure, since it can influence the surface adhesion and thus biofilm formation. Therefore, different materials as cultivation surfaces were investigated as well as the strain specific behavior of different cyanobacteria and the impact on EPS formation. In this work the adhesion of the terrestrial cyanobacteria Coleofasciculus chthonoplastes and Trichocoleus sociatus to different materials was investigated. For characterization of materials measurements concerning surface roughness were conducted using atomic force microscopy. Biofilms were cultivated in an aerosol and the development of surface adhesion in connection with biofilm age was analyzed using two different methods. In the first set-up biofilms were placed in a specially designed flow-through chamber and overflown with medium at increasing flow speed. The detachment of the biofilm was documented with optical coherence tomography (OCT). Additionally, the experiments were supplemented with CFD-simulation for quantification of shear forces. The second method analyzed adhesion forces using rotational rheometry. Hereby, differences between cyanobacteria strains and surface materials could be observed as well as an increasing adhesion with increasing cultivation time. The developed flow-through chamber, which could as well be utilized with a camera instead of OCT, offers a simple low-priced possibility for investigation of surface adhesion.

This project is financially supported by the German Research Foundation (DFG; Project number: UL 170/16-1; MU 2985/3-1 and SFB 926) and the Landesförderung Rheinland-Pfalz (Project: iProcess).