Algae as important environment for bacteria - phylogenetic relationships among species isolated from algae

Bacteria are an inherent part of the biotic environment of algae. Recent investigations revealed that bacterial communities associated with algae were generally highly host specific. Several new bacterial species and genera were isolated from algae, which suggested that algae were an interesting environment for discovery of new bacterial taxa; however, the distribution of the different phylogenetic groups among those isolates remained unclear, and this information could help to explain specific associations. We conducted a phylogenetic study based on 16S rRNA gene sequences available in GenBank, including 101 validly described bacterial species that were isolated from eukaryotic macro- and micro-algae from marine and freshwater environments. These species were distributed among six bacterial phyla, including: Bacteroidetes (42 species), Proteobacteria (36 species), and Firmicutes, Actinobacteria, Verrucomicrobia and Planctomycetes (23 species). Bacterial species and strains that carried out similar metabolic functions were found to colonize similar algal taxa or algal groups. This assumption was supported by information available from bacterial species descriptions: (1) Most of the bacteria described from microalgae grouped into the Roseobacter clade (Alphaproteobacteria), which indicated that members of this group were well adapted for life in close association with phytoplankton; and (2) 32\% of the bacterial species, mainly isolates from macroalgae, were able to decompose macroalgal polysaccharides. Because algal-bacterial association are still under-studied in various algal groups, we expect a great number of new bacterial taxa to be discovered in the future.