Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/23887
Although lichens are generally characterized as the symbiotic association of a fungus (mycobiont) and a photobiont (green algae and/or cyanobacteria), species-specific communitites of other endolichenic bacteria, typically dominated by Proteobacteria, can also be found within the symbiosis. The roles that the non-phototrophic microbiota of lichens play in the symbiotic association is, however, not fully understood. This thesis describes studies that aim to characterize the non-phototrophic microbiota of lichens and elucidate some of their roles in the symbiotic association. Firstly, bacteria were cultured from four saxicolous seashore lichens; Hydropunctaria maura, Verrucaria ceuthocarpa, Caloplaca verruculifera and Lecanora helicopis, which are all commonly found along the Icelandic seashore. A total of 168 strains were isolated and selected isolates were further analysed. Secondly, lichen thalli from the membranous dog lichen, Peltigera membranacea, were investigated using culture-independent techniques, as well as characterizing cultured isolates and some of the roles the constituent bacteria play in the symbiotic association elucidated. Total DNA was extracted and a metagenomic library of 150 thousand contigs constructed and binned against 15 reference genomes. The BlastX algorithm was used for analyses of the selected contigs against the protein database. Taxonomically, the majority of the bacterial associates belong to Alphaproteobacteria, although members of Acidobacteria, Actinobacteria, Bacteroidetes and Verrucomicrobia are also present. Analysis of 28,000 bacterial contigs from the Peltigera membranacea metagenome yielded multiple hits on several genes involved in lichen secondary metabolite resistance, inorganic phosphate mobilization, biopolymer degradation and several other potentially important functions in thallus colonization and symbiosis. Samples of P. membranacea thalli were plated on various media types and 113 bacterial strains isolated. Phenotypic analyses of selected strains indicates that hydrolytic activity is common among these bacteria, as is inorganic phosphate mobilization and nitrogen fixation. Scavenging of organic nutrients may also constitute an important role for Peltigera-associated bacteria, with many of the strains producing strong biosurfactants and being able to degrade naphthalene.
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