Combined eukaryotic and bacterial community fingerprinting of natural freshwater biofilms using automated ribosomal intergenic spacer analysis.

Biofilms are complex communities playing an important role in aquatic ecosystems. Automated ribosomal intergenic spacer analysis (ARISA) has been used successfully to explore biofilm bacterial diversity. However, a gap remains to be filled as regards its application to biofilm eukaryotic populations. The aim of this study is to use ARISA to detect eukaryotic population shifts in biofilm. We designed a new set of primers to focus specifically on the ITS1-5.8S-ITS2 region of diatoms and tested it on natural biofilms. Additionally, we tested universal primers, used previously to perform ARISA on fungal communities. Cloning and sequencing showed that the universal primer set amplified various eukaryotes, whereas the new set was diatom specific. The new set amplified a wider variety of diatoms. Therefore, the universal set is appropriate to study the general eukaryotic population shifts in biofilms, whereas the new set is more appropriate to study diatoms specifically. We used both primer sets, along with a bacterial set, to study the population shifts in natural river biofilms. Principal component analysis of the ARISA fingerprints revealed seasonal shifts that did not coincide for bacterial and eukaryotic communities. Therefore, the use of both eukaryotic and bacterial primers provides a useful insight to assess microbial succession in biofilms.