Twenty-three strains of Rhodococcus equi from independent clinical cases were analyzed for the presence of virulence plasmid DNA. Of the clinical isolates, 19 contained an 85-kb plasmid and the remaining 4 contained a 90-kb plasmid. All of the isolates expressed 15to 17-kDa antigens and were virulent in mice. Restriction enzyme and Southern blot analyses showed large regions of DNA homology between the 85-and 90-kb virulence plasmids. It was concluded tentatively that there are at least two virulence plasmids in R. equi and that they have a common origin.

Background: Senescence is the biological process of age-related cellular and organismal deterioration in function. Results: The transcriptome and metabolome at early stages of replicative senescence of yeast cells were measured. Conclusion: The transcriptomic and metabolomic profiles drastically changed at about half of the average replicative lifespan. Significance: This is the first integrated information on transcriptome and metabolome of aging yeast cells.

The prevalence of virulent Rhodococcus equi in environmental isolates from 31 horse-breeding farms in Hidaka, Hokkaido was investigated: isolates were tested for the presence of virulence plasmid DNA and 15-to 17-kDa antigens by immunoblotting. R. equi was isolated from almost all of the soil samples obtained from the 31 farms with 102 to 105 colony forming units per gram of soil. However, virulent R. equi at various levels (ranging 1.7 to 23.3 %) was isolated from 24 of the 31 farms and appeared in 6.5% of the isolates (121 of 1,865). The ratio of 85-kb and 90-kb virulence Plasmids in the 121 isolates was about 3:1, which was similar to that previously reported about clinical isolates from infected foals in Hidaka. The similarity between the amounts o f virulence Plasmids obtained from the environment and from infected foals indicates that soil-borne virulent R. equi, which is thought to be a major source of the infection, constitutes a great risk to foals in horse-breeding farms. This study shows that plasmid profiles are useful markers in epidemiological surveys of R. equi infection in foals.

Isotope-labeling is a useful technique for understanding cellular metabolism. Recent advances in metabolomics have extended the capability of isotope-assisted studies to reveal global metabolism. For instance, isotope-assisted metabolomics technology has enabled the mapping of a global metabolic network, estimation of flux at branch points of metabolic pathways, and assignment of elemental formulas to unknown metabolites. Furthermore, some data processing tools have been developed to apply these techniques to a non-targeted approach, which plays an important role in revealing unknown or unexpected metabolism. However, data collection and integration strategies for non-targeted isotope-assisted metabolomics have not been established. Therefore, a systematic approach is proposed to elucidate metabolic dynamics without targeting pathways by means of time-resolved isotope tracking, i.e., “metabolic turnover analysis”, as well as multivariate analysis. We applied this approach to study the metabolic dynamics in amino acid perturbation of Saccharomyces cerevisiae. In metabolic turnover analysis, 69 peaks including 35 unidentified peaks were investigated. Multivariate analysis of metabolic turnover successfully detected a pathway known to be inhibited by amino acid perturbation. In addition, our strategy enabled identification of unknown peaks putatively related to the perturbation.

One hundred and eight foals were necropsied and examined for Rhodococcus equi infection from 1992 to 1998 in Hokkaido and