Microsporidia: emerging pathogenic protists

Microsporidia are eukaryotic spore forming obligate intracellular protozoan parasites first recognized over 100 years ago. These organisms infect all of the major animal groups and are now recognized as opportunistic pathogen s of humans. Microsporidian spores are common in the environment and micros poridia pathogenic to humans have been found in water supplies. The genera Nosema, Vittaforma, Brachiola, Pleistophora, Encephalitozoon, Enterocytozoo n. Septata (reclassified to Encephalitozoon and Trachipleistophora have bee n Found in human infections. These organisms have the smallest known eukary otic genomes. Microsporidian ribosomal RNA sequences have proven useful as diagnostic tools as well as for phylogenetic analysis. Recent phylogenetic analysis suggests that Microsporidia are related to the fungi. These organi sms are defined by the presence of a unique invasion organelle consisting o f a single polar tube that coils around the interior of the spore. All micr osporidia exhibit the same response to stimuli, that is, the polar tube dis charges From the anterior pole of the spore in an explosive reaction. If th e polar tube is discharged next to a cell, it can pierce the cell and trans fer its sporoplasm into the cell. A technique was developed for the purific ation of polar tube proteins (PTPs) using differential extraction followed by reverse phase HPLC. This method was used to purify the PTPs from Glugea americanus, Encephalitozoon cuniculi, and Enc. intestinalis. These PTPs dem onstrate conserved characteristics such as solubility hydrophobicity, mass, proline content and immunologic epitopes. The major PTP gene from Enc. cun iculi and Enc. hellem has been cloned and expressed in vitro. The gene sequ ences support the importance of ER and in the formation of the polar tube a s suggested by morphologic studies. Analysis of the cloned proteins also in dicates that secondary structural characteristics are conserved. These char acteristics are probably important in the function of this protein during t he eversion/assembly of the polar tube and in providing elasticity and resi liency for sporoplasm passage. (C) 2001 Elsevier Science B.V. All rights re served.