A glimpse under the rim – the composition of microbial biofilm communities in domestic toilets

The aim of this study was to determine the microbial composition of biofilms in domestic toilets by molecular means. Genomic DNA was extracted from six biofilm samples originating from households around Dusseldorf, Germany. While no archaeal 16S rRNA or fungal ITS genes were detected by PCR, fingerprinting of bacterial 16S rRNA genes revealed a diverse community in all samples. These communities also differed considerably between the six biofilms. Using the Ribosomal Database Project (RDP) classifier tool, 275 cloned 16S rRNA gene sequences were assigned to 11 bacterial phyla and 104 bacterial genera. Only 15 genera (representing 121 sequences affiliated with Acidobacteria, Actinobacteria, Bacteroidetes, Planctomycetes and Proteobacteria) occurred in at least half of the samples or contributed at least 10% of the sequences in a single biofilm. These sequences were defined as ‘typical’ for toilet biofilms, and they were examined in more detail. Virtually all ‘typical’ clones were found to be closely related to bacteria or to sequences obtained from environmental sources, implicating that the flushing water is the main source of recruitment. In view of the great diversity of mostly yet-uncultured bacteria and the considerable differences between individual toilets, very general strategies appear to be most suited for the removal and prevention of toilet biofilms. J Appl Microbiol. 2010;108:1167-74.