53 research outputs found
The Mystery of Two Straight Lines in Bacterial Genome Statistics. Release 2007
In special coordinates (codon position--specific nucleotide frequencies)
bacterial genomes form two straight lines in 9-dimensional space: one line for
eubacterial genomes, another for archaeal genomes. All the 348 distinct
bacterial genomes available in Genbank in April 2007, belong to these lines
with high accuracy. The main challenge now is to explain the observed high
accuracy. The new phenomenon of complementary symmetry for codon
position--specific nucleotide frequencies is observed. The results of analysis
of several codon usage models are presented. We demonstrate that the
mean--field approximation, which is also known as context--free, or complete
independence model, or Segre variety, can serve as a reasonable approximation
to the real codon usage. The first two principal components of codon usage
correlate strongly with genomic G+C content and the optimal growth temperature
respectively. The variation of codon usage along the third component is related
to the curvature of the mean-field approximation. First three eigenvalues in
codon usage PCA explain 59.1%, 7.8% and 4.7% of variation. The eubacterial and
archaeal genomes codon usage is clearly distributed along two third order
curves with genomic G+C content as a parameter.Comment: Significantly extended version with new data for all the 348 distinct
bacterial genomes available in Genbank in April 200
DC-conductivity of a suspension of insulating particles with internal rotation
We analyse the consequences of Quincke rotation on the conductivity of a
suspension. Quincke rotation refers to the spontaneous rotation of insulating
particles dispersed in a slightly conducting liquid and subject to a high DC
electric field: above a critical field, each particle rotates continuously
around itself with an axis pointing in any direction perpendicular to the DC
field. When the suspension is subject to an electric field lower than the
threshold one, the presence of insulating particles in the host liquid
decreases the bulk conductivity since the particles form obstacles to ion
migration. But for electric fields higher than the critical one, the particles
rotate and facilitate ion migration: the effective conductivity of the
suspension is increased. We provide a theoretical analysis of the impact of
Quincke rotation on the apparent conductivity of a suspension and we present
experimental results obtained with a suspension of PMMA particles dispersed in
weakly conducting liquids
Gene size reduction in the bacterial aphid endosymbiont, Buchnera.
International audienc
Re-Evalution du modèle de croissance de Monod. Effet des antibiotiques sur l'énergie de maintenance.
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