Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2000
Publication Date: N/A
Interpretive Summary: All fungi that produce nonmotile spores within an enclosed spore case are classified as Zygomycota. This group of microscopic fungi includes pathogens of pest insects and species that spend much of their life attached to insects and crustaceans. Because they are morphologically simple, determining genetic relationships among these microbes has proven to be nearly impossible using morphology alone. In this study, advances in automated DNA sequencing technologies were used to investigate the evolutionary origin of one arthropod-associated species, Amoebidium parasiticum. By comparing DNA data obtained from this species with that in an international DNA database called GenBank within the National Institutes of Health (NIH), A. parasiticum was found to be a member of a mostly parasitic group of protozoa that infect a wide range of animals including humans. Results of this study suggest that other microbes presently thought to be fungi may actually have evolutionary origins in other groups such as the protozoa. This information has important public health implications because fungi and protozoa may respond very differently to antibiotics.
Technical Abstract: Classification of the Amoebidiales (Trichomycetes, Zygomycota) within the Fungi is problematical because their cell walls apparently lack chitin and they produce amoeboid cells during their life cycle. To examine its phylogenetic relationships, a nearly full-length sequence of the nuclear small subunit (SSU) rRNA of Amoebidium parasiticum was amplified by the polymerase chain reaction (PCR) and sequenced. Results of a BlastN search of GenBank revealed that the A. parasiticum SSU rRNA sequence was most closely related to Ichthyophonus hoferi, an ichthysporean in the Protozoa near the animal-fungal divergence. Maximum parsimony analysis of ichthysporean and fungal SSU sequences, using sequences of choanoflagellates to root the 18S rDNA gene trees, resolved A. parasiticum as a strongly supported sister of I. hoferi within the Ichthyophonida clade of the protozoan class Ichthysporea. In contrast to other members of this class which are mostly obligate or facultative parasites of various animals, A. parasiticum and other members of the Amoebidiales are only known to be arthropodophilous commensals. The results also provide the first evidence that mitochondrial cristae types exhibit homoplastic distributions within the Ichthysporea.