Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2002
Publication Date: 6/1/2003
Citation: Tomaszewski, E.K., Logan, K.E., Snowden, K.F., Kurtzman, C.P., Phalen, D.N. 2003. Phylogenetic analysis identifies the "megabacterium" of birds as a novel anamorphic Ascomycetous yeast, Macrorhabdus ornithogaster gen. nov, sp. nov. International Journal of Systmatic and Evolutionary Microbiology. 53:1201-1205. Interpretive Summary: Microorganisms commonly referred to as "megabacteria" infect domesticated and wild birds. The "megabacteria" are associated with a variety of health problems in birds, including a chronic fatal wasting disease. Because "megabacteria" cannot be grown on laboratory culture media, little is known about these unusual microorganisms. In this study, DNA of "megabacteria" was isolated from infected bird tissue, and a comparison of gene sequences showed the microbial cells to actually be yeasts, not large bacteria as previously believed. Knowing the nature of these microorganisms offers possibilities for treatment of infected birds. This report also describes the bird yeast as Virgamyces avigastricus, a new species placed in a new genus.
Technical Abstract: Organisms commonly referred to as megabacteria colonize the gastric isthmus of many species of birds. They are weakly Gram-positive, PAS-positive, and stain with silver stains. Previous studies show that they have a nucleus and a cell wall similar to that seen in fungi. Calcofluor white M2R staining suggests that their cell wall contains chitin, a eukaryotic-specific product, and rRNA in situ hybridization demonstrates that they are a eukaryote. To phylogenetically characterize this organism, DNA was extracted from purified organisms. RDNA was readily amplified with panfungal DNA primer sets and primer sets derived from the newly determined sequence with PCR, but not with bacterial specific primer sets. Organism-specific primer sets amplified rDNA from isthmus scrapings from an infected bird, but not from a noninfected bird or other control DNA. The sequence was confirmed to derive from the purified organism by in situ rRNA hybridization using a species-specific probe. Phylogenetic analysis of the 18S and domain D1/D2 of 26S rDNA sequences show the organism to be a previously undescribed anamorphic ascomycetous yeast representing a new genus. We propose to name this organism Virgamyces avigastricus.