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The genetic diversity of Cryptosporidium spp. and Giardia duodenalis from dairy cattle and pigs in Denmark was determined in the present study. Faecal samples from 1237 pigs and 1150 cattle originating from 50 sow herds and 50 dairy herds, respectively, were analysed for the presence of the two parasites by immunofluorescence microscopy. A large proportion of the (oo)cyst containing samples were selected for molecular characterization. Sequencing and phylogenetic analysis of the 18S rDNA locus and/or the HSP70 gene of 183 pig and 154 cattle isolates of Cryptosporidium revealed the presence of C. suis, pig genotype II, C. parvum (cattle genotype), C. bovis, Cryptosporidium deer-like genotype and a novel C. suis-like genotype. For both cattle and pigs, a host age-related change in distribution of species/genotypes was observed. The zoonotic C. parvum (cattle genotype) was most prevalent in young calves. For Giardia, 82 and 145 isolates from pigs and cattle, respectively, were analysed at the 18S rDNA locus and/or the gdh gene. Giardia isolates belonging to the zoonotic Assemblage A was found in both young and older calves, as well as in weaners and piglets, whereas cows seemed to be infected purely by isolates of the livestock group, Assemblage E.

Gene redundancy has been observed in yeast, plant and human genomes, and is thought to be a consequence of whole-genome duplications. Baker's yeast, Saccharomyces cerevisiae, contains several hundred duplicated genes. Duplication(s) could have occurred before or after a given speciation. To understand the evolution of the yeast genome, we analysed orthologues of some of these genes in several related yeast species. On the basis of the inferred phylogeny of each set of genes, we were able to deduce whether the gene duplicated and/or specialized before or after the divergence of two yeast lineages. Here we show that the gene duplications might have occurred as a single event, and that it probably took place before the Saccharomyces and Kluyveromyces lineages diverged from each other. Further evolution of each duplicated gene pair-such as specialization or differentiation of the two copies, or deletion of a single copy--has taken place independently throughout the evolution of these species.

SummaryFor decades, unicellular yeasts have been general models to help understand the eukaryotic cell and also our own biology. Recently, over a dozen yeast genomes have been sequenced, providing the basis to resolve several complex biological questions. Analysis of the novel sequence data has shown that the minimum number of genes from each species that need to be compared to produce a reliable phylogeny is about 20. Yeast has also become an attractive model to study speciation in eukaryotes, especially to understand molecular mechanisms behind the establishment of reproductive isolation. Comparison of closely related species helps in gene annotation and to answer how many genes there really are within the genomes. Analysis of non-coding regions among closely related species has provided an example of how to determine novel gene regulatory sequences, which were previously difficult to analyse because they are short and degenerate and occupy different positions. Comparative genomics helps to understand the origin of yeasts and points out crucial molecular events in yeast evolutionary history, such as whole-genome duplication and horizontal gene transfer(s). In addition, the accumulating sequence data provide the background to use more yeast species in model studies, to combat pathogens and for efficient manipulation of industrial strains.

The complete sequences of mitochondrial DNA (mtDNA) from the two budding yeasts Saccharomyces castellii and Saccharomyces servazzii, consisting of 25 753 and 30 782 bp, respectively, were analysed and compared to Saccharomyces cerevisiae mtDNA. While some of the traits are very similar among Saccharomyces yeasts, others have highly diverged. The two mtDNAs are much more compact than that of S.cerevisiae and contain fewer introns and intergenic sequences, although they have almost the same coding potential. A few genes contain group I introns, but group II introns, otherwise found in S.cerevisiae mtDNA, are not present. Surprisingly, four genes (ATP6, COX2, COX3 and COB) in the mtDNA of S.servazzii contain, in total, five +1 frameshifts. mtDNAs of S.castellii, S.servazzii and S.cerevisiae contain all genes on the same strand, except for one tRNA gene. On the other hand, the gene order is very different. Several gene rearrangements have taken place upon separation of the Saccharomyces lineages, and even a part of the transcription units have not been preserved. It seems that the mechanism(s) involved in the generation of the rearrangements has had to ensure that all genes stayed encoded by the same DNA strand.