Higher Gene Duplicabilities for Metabolic Proteins Than for Nonmetabolic Proteins in Yeast and <Emphasis Type="Italic">E. coli</Emphasis>

Although the evolutionary significance of gene duplication has long been appreciated, it remains unclear what factors determine gene duplicability. In this study we investigated whether metabolism is an important determinant of gene duplicability because cellular metabolism is crucial for the survival and reproduction of an organism. Using genomic data and metabolic pathway data from the yeast (Saccharomyces cerevisiae) and Escherichia coli, we found that metabolic proteins indeed tend to have higher gene duplicability than nonmetabolic proteins. Moreover, a detailed analysis of metabolic pathways in these two organisms revealed that genes in the central metabolic pathways and the catabolic pathways have, on average, higher gene duplicability than do other genes and that most genes in anabolic pathways are single-copy genes.Reviewing Editor: Dr. Rüdiger Cerff     

Shewanella khirikhana sp. nov. – a shrimp pathogen isolated from a cultivation pond exhibiting early mortality syndrome

Early mortality syndrome (EMS) in cultivated shrimp is of complex aetiology. One of the causes is acute hepatopancreatic necrosis disease (AHPND) caused by unique Vibrio isolates that carry two Pir^vp toxin genes, but other causes of EMS remain mostly unexplained. Here, we describe the discovery of a Shewanella isolate TH2012^T from an EMS/AHPND outbreak pond and demonstrate its virulence for shrimp (the mean lethal concentration of 10⁵ colony-forming units per millilitre by immersion challenge) accompanied by distinctive histopathology, particularly of the ventral nerve cord and lymphoid organ but also including the digestive tract. On the basis of its complete genome sequence, multilocus phylogenetic trees, digital DNA–DNA hybridization analysis and differential phenotypic characteristics, we propose that Shewanella isolate TH2012^T represents a novel species, separated sufficiently from the type strains S. litorisediminis and S. amazonensis to justify naming it Shewanella khirikhana sp. nov. Analysis of the TH2012^T genome revealed no homologues of the Pir^vp toxin genes but revealed a number of other potential virulence factors. It constitutes the first Shewanella isolate reported to be pathogenic to shrimp.     

Intron size correlates positively with recombination rate in Caenorhabditis elegans

A negative correlation between intron size and recombination rate has been reported for the Drosophila melanogaster and human genomes. Population-genetic models suggest that this pattern could be caused by an interaction between recombination rate and the efficacy of natural selection. To test this idea, we examined variation in intron size and recombination rate across the genome of the nematode Caenorhabditis elegans. Interestingly, we found that intron size correlated positively with recombination rate in this species.     

Complete genome sequence of virulence-enhancing Siphophage VHS1 from Vibrio harveyi

Vibrio harveyi siphophage 1 (VHS1) is a tailed phage with an icosahedral head of approximately 66 nm in diameter and an unornamented, flexible tail of approximately 153 nm in length. When Vibrio harveyi 1114GL is lysogenized with VHS1, its virulence for the black tiger shrimp (Penaeus monodon) increases by more than 100 times, and this coincides with production of a toxin(s) associated with shrimp hemocyte agglutination. Curiously, the lysogen does not show increased virulence for the whiteleg shrimp (Penaeus [Litopenaeus] vannamei). Here we present and annotate the complete, circular genome of VHS1 (81,509 kbp; GenBank accession number JF713456). By software analysis, the genome contains 125 putative open reading frames (ORFs), all of which appear to be located on the same DNA strand, similar to the case for many other bacteriophages. Most of the putative ORFs show no significant homology to known sequences in GenBank. Notable exceptions are ORFs for a putative DNA polymerase and putative phage structural proteins, including a portal protein, a phage tail tape measure protein, and a phage head protein. The last protein was identified as a component of the species-specific toxin mixture described above as being associated with agglutination of hemocytes from P. monodon.