Human parasite finds taxonomic home

Karyotypic diversity among Blastocystis hominis isolates

Fifteen Blastocystis hominis strains, 13 axenic and 2 monoxenic, have been included in the present study. The chromosomal pattern was analyzed by the contour-clamped homogeneous electric-field (CHEF) system. The number of chromosomes detected ranged between 9 and 13, with sizes from 2200 kbp to 260 kbp. Eleven karyotypic profiles, with a common pattern constituted by 8 chromosomes of 2200, 1280, 890, 840, 700, 650, 540 and 260 kbp, were observed. The Jaccard index demonstrated that the similarity between isolates ranged from 0.5714 to 1. The different isolates were clustered in 3 karyotypes (A: 8 isolates; B: 6 isolates and C: 1 isolate). All isolates grouped in karyotype A presented a characteristic band of 730 kbp, whereas in the isolate of karyotype C the 810-kbp band was not observed.

Riboprinting: a tool for the study of genetic diversity in microorganisms

Classical morphology-based methods of taxonomic and phylogenetic analysis are inadequate in many groups of structurally simple eukaryotes. Molecular methods can generate data independently of the complexity of the organisms' morphology. Riboprinting is one such technique, and involves restriction enzyme analysis of polymerase chain reaction amplified small subunit ribosomal RNA genes. The utility of the method is illustrated with examples from several genera of intestinal and bloodstream parasites. Among the applications of riboprinting are the detection of cryptic genetic variation within species, organism misidentifications and culture mix-ups, independent verification of DNA sequences, and the rapid generation of data useful in phylogenetic analyses.

Extensive genetic diversity in Blastocystis hominis

Blastocystis homonis is a common human parasite of uncertain role in human disease. Approximately equal numbers of reports implicate it and exonerate it as a pathogen. Genetic diversity in B. hominis was investigated using riboprinting to study sequence variation in the small subunit ribosomal RNA genes of 30 randomly selected isolates. Extensive sequence variation was discovered in B. hominis ribosomal RNA genes and this species consists of at least seven morphologically identical but genetically quite distinct organisms. If only a subset of the B. hominis variants have the potential to cause disease in humans this might explain the disparate findings reported. Future clinical studies must take the heterogeneity of B. hominis into account.

Biodiversity, genomes, and DNA sequence databases

There are approximately 1.4 million organisms on this planet that have been described morphologically but there is no comparable coverage of biodiversity at the molecular level. Little more than 1% of the known species have been subject to any molecular scrutiny and eukaryotic genome projects have focused on a group of closely related model organisms. The past year, however, has seen an approximately 80% increase in the number of species represented in sequence databases and the completion of the sequencing of three prokaryotic genomes. Large-scale sequencing projects seem set to begin coverage of a wider range of the eukaryotic diversity, including green plants, microsporidians and diplomonads.