Molecular evolution in the gnd locus of Salmonella enterica |
| |
Authors: | Thampapillai G; Lan R; Reeves PR |
| |
Institution: | Department of Microbiology, University of Sydney, New South Wales, Australia. |
| |
Abstract: | The gnd gene, the structural gene for 6-phosphogluconate dehydrogenase, was
sequenced and analyzed in 34 isolates from different serovars of the seven
subspecies of Salmonella enterica to provide comparative information on the
evolution in this gene, which has been studied extensively in Escherichia
coli. The gene tree obtained by the neighbor- joining method in general
gave separate branches for each subspecies, with the few exceptions readily
explained by recombination. There is evidence of recombination involving
transfer of long (more than 400 bp) and short (30-150 bp) segments of DNA.
Four of the six long-segment transfers detected are at the 5' end of the
gene, and in all four cases a variant of the chi sequence is located close
to the recombination junction and appears to have mediated the
recombination events. We suggest that in these four cases and in a fifth
case with intersubspecies transfer of the whole gnd gene, the adjacent rfb
(O antigen) locus may have been transferred in the same event. The
estimates of the number of synonymous substitutions per synonymous site,
KS, and the number of nonsynonymous substitutions per nonsynonymous site,
KA, within the E. coli and S. enterica gnd genes, and also between the two
species show an interesting distribution, with KS being lower toward the
ends of the gene and KA in particular being lower in the first than in the
second domain. In S. enterica, synonymous sites also seem to be subjected
to negative selection. The ratio of KA to KS was higher within S. enterica
and E. coli than between them, which may indicate that intraspecies
variation is essentially between clones and that mildly deleterious
mutations can be fixed within clones, which would thus raise KA within
species.
|
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|