Genetic characterization of microbial communities living at the surface of building stones

The aim of the present study was to reveal the microbial genetic diversity of epilithic biofilms using a DNA-based procedure.

A DNA extraction protocol was first selected to obtain PCR-amplifiable metagenomic DNA from a limestone biofilm. Extracted DNA was used to amplify either 16S rRNA genes or ITS regions from prokaryotic and eukaryotic genomes, respectively. Amplified DNAs were subsequently cloned, amplified by colony PCR and screened by restriction analysis [restriction analyses of amplified ribosomal DNA (ARDRA)] for DNA sequencing. Phylogenetic analysis using 16S rDNA sequences showed that predominating bacteria were Alphaproteobacteria belonging to the genera Sphingomonas, Erythrobacter, Porphyrobacter, Rhodopila and Jannashia; Cyanobacteria and Actinobacteria were also identified. Analysis of ITS rDNA sequences revealed the presence of algae of the Chlorophyceae family and fungi related either to Rhinocladiella or to a melanized ascomycete. Statistical analysis showed that the specific richness evidenced was representative of the original sampled biofilm.

The molecular methodology developed here constitutes a valuable tool to investigate the genetic diversity of microbial biofilms from building stone.

The easy-to-run molecular method described here has practical importance to establish microbiological diagnosis and to define strategies for protection and restoration of stone surfaces.