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High rate of mobilization for blaCTX-Ms.

Barlow M, Reik RA, Jacobs SD, Medina M, Meyer MP, McGowan JE, Tenover FC - Emerging Infect. Dis. (2008)

Bottom Line: We also found that the blaCTX-Ms are descended from a common ancestor that was incorporated in ancient times into the chromosome of the ancestor of Kluyvera species through horizontal transfer.Considerable sequence divergence has occurred among the descendents of that ancestral gene sequence since that gene was inserted.That divergence has mainly occurred in the presence of purifying selection, which indicates a slow rate of evolution for blaCTX-Ms in the pre-antimicrobial drug era.

View Article: PubMed Central - PubMed

Affiliation: University of California, Merced, California 95344, USA. mbarlow@ucmerced.edu

ABSTRACT
We constructed a phylogenetic analysis of class A beta-lactamases and found that the blaCTX-Ms have been mobilized to plasmids approximately 10 times more frequently than other class A beta-lactamases. We also found that the blaCTX-Ms are descended from a common ancestor that was incorporated in ancient times into the chromosome of the ancestor of Kluyvera species through horizontal transfer. Considerable sequence divergence has occurred among the descendents of that ancestral gene sequence since that gene was inserted. That divergence has mainly occurred in the presence of purifying selection, which indicates a slow rate of evolution for blaCTX-Ms in the pre-antimicrobial drug era.

Show MeSH
Phylogenetic analysis of blaCTX-Ms. This tree was calculated by Bayesian inference. Number of mutations occurring along each branch are given along the length of the branch. Black dots represent mobilizations. Boldface indicates chromosomal genes. CTX-M-14 and 3a exist as both unmobilized chromosomal genes and plasmid-borne CTX-M alleles.
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Figure 1: Phylogenetic analysis of blaCTX-Ms. This tree was calculated by Bayesian inference. Number of mutations occurring along each branch are given along the length of the branch. Black dots represent mobilizations. Boldface indicates chromosomal genes. CTX-M-14 and 3a exist as both unmobilized chromosomal genes and plasmid-borne CTX-M alleles.

Mentions: Estimation of the nonsynonymous (dN) and synonymous (dS) substitution rates is an important means of understanding mechanisms of molecular evolution. A dN/dS ratio >1 is taken as evidence of positive selection, whereas a dN/dS ratio <1 is taken as evidence of purifying selection (25). The Codeml program of the PAML package (available from http://envgen.nox.ac.uk/bioinformatics/docs/codeml.html) (25) was used to estimate dN/dS ratios in the phylogenetic analysis shown in Figure 1. The values were calculated by using model 1 in the program, and default parameters were used for the execution of the program.


High rate of mobilization for blaCTX-Ms.

Barlow M, Reik RA, Jacobs SD, Medina M, Meyer MP, McGowan JE, Tenover FC - Emerging Infect. Dis. (2008)

Phylogenetic analysis of blaCTX-Ms. This tree was calculated by Bayesian inference. Number of mutations occurring along each branch are given along the length of the branch. Black dots represent mobilizations. Boldface indicates chromosomal genes. CTX-M-14 and 3a exist as both unmobilized chromosomal genes and plasmid-borne CTX-M alleles.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2570810&req=5

Figure 1: Phylogenetic analysis of blaCTX-Ms. This tree was calculated by Bayesian inference. Number of mutations occurring along each branch are given along the length of the branch. Black dots represent mobilizations. Boldface indicates chromosomal genes. CTX-M-14 and 3a exist as both unmobilized chromosomal genes and plasmid-borne CTX-M alleles.
Mentions: Estimation of the nonsynonymous (dN) and synonymous (dS) substitution rates is an important means of understanding mechanisms of molecular evolution. A dN/dS ratio >1 is taken as evidence of positive selection, whereas a dN/dS ratio <1 is taken as evidence of purifying selection (25). The Codeml program of the PAML package (available from http://envgen.nox.ac.uk/bioinformatics/docs/codeml.html) (25) was used to estimate dN/dS ratios in the phylogenetic analysis shown in Figure 1. The values were calculated by using model 1 in the program, and default parameters were used for the execution of the program.

Bottom Line: We also found that the blaCTX-Ms are descended from a common ancestor that was incorporated in ancient times into the chromosome of the ancestor of Kluyvera species through horizontal transfer.Considerable sequence divergence has occurred among the descendents of that ancestral gene sequence since that gene was inserted.That divergence has mainly occurred in the presence of purifying selection, which indicates a slow rate of evolution for blaCTX-Ms in the pre-antimicrobial drug era.

View Article: PubMed Central - PubMed

Affiliation: University of California, Merced, California 95344, USA. mbarlow@ucmerced.edu

ABSTRACT
We constructed a phylogenetic analysis of class A beta-lactamases and found that the blaCTX-Ms have been mobilized to plasmids approximately 10 times more frequently than other class A beta-lactamases. We also found that the blaCTX-Ms are descended from a common ancestor that was incorporated in ancient times into the chromosome of the ancestor of Kluyvera species through horizontal transfer. Considerable sequence divergence has occurred among the descendents of that ancestral gene sequence since that gene was inserted. That divergence has mainly occurred in the presence of purifying selection, which indicates a slow rate of evolution for blaCTX-Ms in the pre-antimicrobial drug era.

Show MeSH