Isolation and Molecular characterization of planktonic and epilithic bacterial communities from the iron-rich river Acquarossa

Background: Acquarossa river (Viterbo, Italy) is a peculiar riparian ecological niche in the volcanic area of central Italy, characterized by high level of iron deposition and geothermal activity. There are biological, geochemical, and biotechnological reasons to analyze microbial populations in such extreme environments and to understand their ecology. Besides, epilithons are biofilms which develops on the surface of stones in aquatic habitats. They have a complex structure, consisting of prokaryotes, fungi, and protists together within a polysaccharide matrix. Objectives: The isolation and the molecular characterisation of bacterial communities were performed in order to: i) compare the biodiversity of the different ecological niches, ii) individuate bacterial functional group, able to thrive and to modify such extreme environments iii) study the horizontal gene transfer (HGT) in the epilithons as they provide an environment where sessile bacterial populations and high levels of activity can promote bacterial interactions. Methods: Cultivable bacteria were isolated from the sediment, the water in the river stream and from two epilithons forming on the river canyon rocks; 16 rDNA sequencing of 500 randomly selected isolated was performed followed by sequence analyses and phylogenetic trees construction. Conclusions: Analyses pointed out a high level of biodiversity in the river but with a strong prevalence (50%) of bacteria of the Proteobacteria phylum (in particular gamma-proteobacteria). Bacteria with peculiar bio-geochemical roles were identified. In the two epilithons, 56% and 87% of isolated bacteria belongs to the genus Acinetobacter, suggesting peculiar ecological dynamics in these semi-sessile communities.