Bacterial symbionts that inhabit apothecia of the cup fungus Scutellinia scutellata

New symbiotic relationships between bacteria and members of all other eukaryotic Kingdoms - Plant, Animal, Fungal and Protist - are continually being discovered. Higher resolution imaging of eukaryotic tissues is revealing that coexistence of live bacteria among cells of eukaryotic tissues is more ubiquitous than has been conventionally reported. Apothecia of the discomycete fungus Scutellinia scutellata are colonized by extracellular bacteria throughout their primary tissue types as viewed in thin sections of both tissues and in scanning electron microscope images of the hymenial surface. Within the hymenium, at the termination of ascosporogenesis, these bacteria invade each ascus and associate with surfaces of mature ascospores. DNA was extracted from intact S. scutellata, and approximately 1500 bp of the 16S ribosomal RNA gene was amplified using general eubacterial primers. DNA sequences of the predominant bacteria found in association with S. scutellata do not correspond to sequences of bacteria reported from endophytic, mycorrhizal, or other fungi but surprisingly closely match sequences of members of the genera Acidovorax and Verminephrobacter, the latter being beneficial extracellular symbionts of earthworm nephridia. From a total of 74 non-chimeric clones sequenced, 52% had a high similarity to free-living Acidovorax bacteria (97 to 99% identity) and to members of the genus Verminephrobacter (95% identity), until recently also placed in the genus Acidovorax. All attempts to culture hyphae in the absence of bacteria failed. To our knowledge, this represents the first report of these versatile Acidovorax-like bacteria having established symbiotic relationships with members of both Fungal and Animal Kingdoms.