Cryptosporidium and Giardia in different age groups of Danish cattle and pigs--occurrence and management associated risk factors.

To obtain information both about the prevalence of Giardia and Cryptosporidium in Danish cattle and pigs as well as the possible influence of different management systems on the occurrence and intensity of infection, we conducted an epidemiological survey comprising 50 randomly selected dairy and sow herds, respectively. Each herd was visited once for the collection of faecal samples and registration of basic management parameters. Faecal samples were collected from three different age groups of animals, i.e. 5 sows/cows, 10 nursing piglets/calves less than 1 month, and 10 weaner pigs 8-45 kg/calves 1-12 months. The faecal samples were purified and the number of (oo)cysts quantified. The study revealed an age-specific herd prevalence of Cryptosporidium of 16, 31 and 100% for sows, piglets and weaners, respectively, and of 14, 96 and 84% for cows, young calves and older calves, respectively. For Giardia the age-specific herd prevalence was 18, 22 and 84% for the sows, piglets and weaners, while for cattle herds the prevalence was 60, 82 and 100% for cows, young calves and older calves, correspondingly. The (oo)cyst excretion levels varied considerably both within and between herds for all age groups. Risk factors were evaluated by using proportional odds models with (oo)cyst excretion levels divided into four categories as response. Among the numerous risk factors examined, only a few were demonstrated to have a statistically significant influence, e.g. the use of an empty period in the calf pen between introduction of calves for both parasites had a protective effect in young calves. For weaners, use of straw in the pen and high pressure cleaning between batches of weaners had a preventive effect against higher Cryptosporidium oocyst excretion levels.

Yeast genome sequencing: the power of comparative genomics.

For 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.

High-rate evolution of Saccharomyces sensu lato chromosomes.

Forty isolates belonging to the Saccharomyces sensu lato complex were analyzed for one nuclear and two mitochondrial sequences, and for their karyotypes. These data are useful for description and definition of yeast species based on the phylogenetic species concept. The deduced phylogenetic relationships among isolates based on the nuclear and mitochondrial sequences were usually similar, suggesting that horizontal transfer/introgression has not been frequent. The highest degree of polymorphism was observed at the chromosome level. Even isolates which had identical nuclear and mitochondrial sequences often exhibited variation in the number and size of their chromosomes. Apparently, yeast chromosomes have been frequently reshaped and therefore also the position of genes has been dynamic during the evolutionary history of yeasts.

Yeast genome duplication was followed by asynchronous differentiation of duplicated genes.

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.

Inheritance and organisation of the mitochondrial genome differ between two Saccharomyces yeasts.

Petite-positive Saccharomyces yeasts can be roughly divided into the sensu stricto, including Saccharomyces cerevisiae, and sensu lato group, including Saccharomyces castellii; the latter was recently studied for transmission and the organisation of its mitochondrial genome. S. castellii mitochondrial molecules (mtDNA) carrying point mutations, which confer antibiotic resistance, behaved in genetic crosses as the corresponding point mutants of S. cerevisiae. While S. castellii generated spontaneous petite mutants in a similar way as S. cerevisiae, the petites exhibited a different inheritance pattern. In crosses with the wild type strains a majority of S. castellii petites was neutral, and the suppressivity in suppressive petites was never over 50%. The two yeasts also differ in organisation of their mtDNA molecules. The 25,753 bp sequence of S. castellii mtDNA was determined and the coding potential of both yeasts is similar. However, the S. castellii intergenic sequences are much shorter and do not contain sequences homologous to the S. cerevisiae biologically active intergenic sequences, as ori/rep/tra, which are responsible for the hyper-suppressive petite phenotype found in S. cerevisiae. The structure of one suppressive S. castellii mutant, CA38, was also determined. Apparently, a short direct intergenic repeat was involved in the generation of this petite mtDNA molecule.