A microbiotic survey of lichen-associated bacteria reveals a new lineage from the Rhizobiales

This study uses a set of PCR-based methods to examine the putative microbiota associated with lichen thalli. In initial experiments, generalized oligonucleotide-primers for the 16S rRNA gene resulted in amplicon pools populated almost exclusively with fragments derived from lichen photobionts (i.e., Cyanobacteria or chloroplasts of algae). This effectively masked the presence of other lichen-associated prokaryotes. In order to facilitate the study of the lichen microbiota, 16S ribosomal oligonucleotide-primers were developed to target Bacteria, but exclude sequences derived from chloroplasts and Cyanobacteria. A preliminary microbiotic survey of lichen thalli using these new primers has revealed the identity of several bacterial associates, including representatives of the extremophilic Acidobacteria, bacteria in the families Acetobacteraceae and Brucellaceae, strains belonging to the genus Methylobacterium, and members of an undescribed lineage in the Rhizobiales. This new lineage was investigated and characterized through molecular cloning, and was found to be present in all examined lichens that are associated with green algae. There is evidence to suggest that members of this lineage may both account for a large proportion of the lichen-associated bacterial community and assist in providing the lichen thallus with crucial nutrients such as fixed nitrogen.