Biofilms

The predominant lifestyle of microbes in the environment is the 'biofilm-mode of life', an existence in cellular aggregates attached to a solid surface and embedded in a self-produced slime.

Suspended biofilms of Pseudomonas aeruginosa

We demonstrated that the 'biofilm-mode of life' of the biofilm-model organism Pseudomonas aeruginosa is also reflected in standard liquid cultures, which have traditionally been described as planktonic, individual-cell cultures. In fact, the plankton in shaken liquid cultures is composed of biofilms, here, of suspended biofilms: up to 90% of the total planktonic biomass consists of cellular aggregates (20-400 μm) during the growth phase, as opposed to individual cells (2-4 µm). Further, once these aggregated cultures enter stationary phase due to starvation, the aggregates disperse into single cells, and this affects an additional increase of optical density (OD) independent of cellular growth!

Our observations published in PLoS ONE appeared that the suspended biofilms formed in planktonic cultures of P. aeruginosa share many of the same features as the surface associated biofilms, including their dependencies on cyclic di-GMP, eDNA, bacteriophage, and dispersal based on carbon, nitrogen, or oxygen limitations. The observations hold important implications for future studies of P. aeruginosa, and moreover, can consistently be exploited in future studies of biofilm formation and dispersal processes.

Photoautotrophic–heterotrophic biofilm communities:
growing axenic diatoms and bacteria in defined mixed-species biofilms

Biofilm communities in the euphotic zone of aquatic habitats comprise photoautotrophic microorganisms, such as diatoms, green algae and cyanobacteria, which produce the organic carbon that fuels the life of a heterotrophic contingent of microorganisms, mostly bacteria. Such photoautotrophic–heterotrophic mixed-species biofilms have received little attention in biofilm research due to a lack of suitable pure-culture laboratory model systems. In cooperation with Dr. Matthias Buhmann and Prof. Peter Kroth at University of Konstanz, we developed a sterile incubation chamber for growing and monitoring axenic phototrophic biofilms in the laboratory, i.e., a sterilizable, illuminated, continuous-flow system for a routine work with pure cultures.

Anti-biofilm strategies:
Exploration of novel nanoparticle systems

There is a huge demand for innovative surface coatings that provide intrinsic and highly effective antibacterial activity, in order to prevent surface colonization and biofilm formation (biofouling), e.g., in medical, industrial and environmental settings. In cooperation with Dr. Julia Gehring and Prof. Sebastian Polarz, Chemistry Department of University of Konstanz, we introduced and tested a new, sunlight-mediated organosilica nanoparticle (NP) system based on silver-free antibacterial activity. The simultaneous release of nitric oxide (NO) in combination with singlet oxygen and superoxide radicals (O2^•-) as reactive oxygen species (ROS) leads to the emergence of highly reactive peroxynitrite molecules with significantly enhanced biocidal activity. The high antibacterial efficiency of these dual-action nanoparticles was demonstrated using assays with the pathogenic biofilm-forming bacterium Pseudomonas aeruginosa, as published in Journal of the American Chemical Society (JACS). Earlier work done in cooperation involved also mesoporous organosilica nanoparticles with highly reactive, superacidic sulfonic-acid surfaces, as published in Advanced Functional Materials.