Contrasting Pediatric and Adult Methicillin-resistant Staphylococcus aureus Isolates

Children may share a reservoir of MRSA strains that have an antimicrobial drug resistance profile distinct from that of adults

Inferring Genome Trees by Using a Filter To Eliminate Phylogenetically Discordant Sequences and a Distance Matrix Based on Mean Normalized BLASTP Scores

Darwin's paradigm holds that the diversity of present-day organisms has arisen via a process of genetic descent with modification, as on a bifurcating tree. Evidence is accumulating that genes are sometimes transferred not along lineages but rather across lineages. To the extent that this is so, Darwin's paradigm can apply only imperfectly to genomes, potentially complicating or perhaps undermining attempts to reconstruct historical relationships among genomes (i.e., a genome tree). Whether most genes in a genome have arisen via treelike (vertical) descent or by lateral transfer across lineages can be tested if enough complete genome sequences are used. We define a phylogenetically discordant sequence (PDS) as an open reading frame (ORF) that exhibits patterns of similarity relationships statistically distinguishable from those of most other ORFs in the same genome. PDSs represent between 6.0 and 16.8% (mean, 10.8%) of the analyzable ORFs in the genomes of 28 bacteria, eight archaea, and one eukaryote (Saccharomyces cerevisiae). In this study we developed and assessed a distance-based approach, based on mean pairwise sequence similarity, for generating genome trees. Exclusion of PDSs improved bootstrap support for basal nodes but altered few topological features, indicating that there is little systematic bias among PDSs. Many but not all features of the genome tree from which PDSs were excluded are consistent with the 16S rRNA tree

An archaebacterial homolog of pelota, a meiotic cell division protein in eukaryotes

An open reading frame (pelA) specifying a homolog of pelota and DOM34, proteins required for meiotic cell division in Drosophila melanogaster and Saccharomyces cerevisiae, respectively, has been cloned, sequenced and identified from the archaebacterium Sulfolobus solfataricus. The S. solfataricus PelA protein is about 20% identical with pelota, DOM34 and the hypothetical protein R74.6 of Caenorhabditis elegans. The presence of a pelota homolog in archaebacteria implies that the meiotic functions of the eukaryotic protein were co-opted from, or added to, other functions existing before the emergence of eukaryotes. The nuclear localization signal and negatively charged carboxy-terminus characteristic of eukaryotic pelota-like proteins are absent from the S. solfataricus homolog, and hence may be indicative of the acquired eukaryotic function(s)