Biomass samples were collected from the three different incubators at the moment that the biofilms reached their mature stage. microcosms) located at three different laboratories in Europe were inoculated with the same environmental biofilm sample at the same time and operated under exactly the same conditions. In the current study identical open flow-lane incubator systems (i.e. In most cases these systems were used to study single-species biofilms or mixed biofilms with a predefined community composition. Since biofilm communities in nature are often difficult to investigate and experimental conditions are ambiguous, a number of different laboratory-based experimental biofilm model systems have been developed ( Palmer, 1999 Heydorn et al., 2000 Jackson et al., 2001). In order to enhance our understanding of the complex phototrophic biofilm physiology, the individual community members should not be studied separately. The study of artificial phototrophic biofilms may also increase our understanding of the development of more complex phototrophic biofilms, such as microbial mats and stromatolites ( Des Marais, 1990). bioremediation ( Schumacher et al., 2003), aquaculture ( Bender & Phillips, 2004) and biohydrogen production ( Prince & Kheshgi, 2005). There is a growing interest in the application of phototrophic biofilms, e.g. The microorganisms produce extracellular polymeric substances (EPS) that hold the biofilm together ( Wimpenny et al., 2000 Cogan & Keener, 2004). Their oxygenic photosynthetic activity fuels metabolic processes and conversions in the entire biofilm community, including the heterotrophic fraction ( Paerl et al., 2000). Diatoms, green algae and cyanobacteria are the major primary producers that generate energy and reduce carbon dioxide, providing organic substrate and oxygen.

They can best be described as surface-attached microbial communities driven by light as energy source. Phototrophic biofilms occur on contact surfaces in a range of terrestrial and aquatic environments. But until recently phototrophic biofilms have received little attention for this aspect. Structure, growth dynamics and physiology of heterotrophic biofilms have been extensively studied. In the present study, cultivated phototrophic biofilms were chosen as a model to assess reproducibility. Hence, it is surprising that reproducibility assessments are scarcely documented in the literature (e.g. Reproducibility is indisputably essential to validate the use of microcosm systems in microbial ecology studies. These simplified systems can still contain a high diversity of species and therefore require self-organizing processes to reach and maintain system stability ( Odum, 1989 Kangas & Adey, 1996).

Hence, microcosm studies can be very useful to study the effects of disturbance or to determine the role of key species. They provide an experimental area for ecologists to study natural processes. Microcosms are constructed, simplified ecosystems that are used to mimic natural ecosystems under controlled conditions. These findings demonstrate that validation of reproducibility is essential for the use of microcosm systems in microbial ecology studies.īiofilm, cyanobacteria, DGGE, microbial ecology, oxygenic phototrophs Introduction In addition, DGGE profiles obtained from the cultivated biofilms showed a low resemblance with the profiles derived from the inoculum. No clear effect of light intensity on the cyanobacterial community composition was observed. One microcosm was dominated by Microcoleus and Phormidium species, the second microcosm was dominated by Synechocystis and Phormidium species, and the third microcosm was dominated by Microcoleus- and Planktothrix-affiliated species. The growth rates of the biofilms were similar in the different microcosms, but denaturing gradient gel electrophoresis (DGGE) analysis of both 16S and 18S rRNA gene fragments showed that the communities developed differently in terms of species richness and community composition. Phototrophic biofilms were cultivated simultaneously using the same inoculum in three identical flow-lane microcosms located in different laboratories.

Microcosm flow