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Glutamine synthetase sequence evolution in the mycobacteria and their use as molecular markers for Actinobacteria speciation.

Hayward D, van Helden PD, Wiid IJ - BMC Evol. Biol. (2009)

Bottom Line: Intriguingly, previous reports have shown that only one copy (glnA1) is essential for growth in M. tuberculosis, while the other copies (glnA2, glnA3 and glnA4) are not.In this report it is shown that the glnA1 and glnA2 encoded glutamine synthetase sequences were inherited from an Actinobacteria ancestor, while the glnA4 and glnA3 encoded GS sequences were sequentially acquired during Actinobacteria speciation.Different selective pressures by the ecological niche that the organisms occupy may influence the sequence evolution of glnA1 and glnA2 and thereby affecting phylogenies based on the protein sequences they encode.

View Article: PubMed Central - HTML - PubMed

Affiliation: DST/NRF Centre for Excellence in Biomedical Tuberculosis Research, US/MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Faculty of Health Sciences - Stellenbosch University, South Africa. dh@sun.ac.za

ABSTRACT

Background: Although the gene encoding for glutamine synthetase (glnA) is essential in several organisms, multiple glnA copies have been identified in bacterial genomes such as those of the phylum Actinobacteria, notably the mycobacterial species. Intriguingly, previous reports have shown that only one copy (glnA1) is essential for growth in M. tuberculosis, while the other copies (glnA2, glnA3 and glnA4) are not.

Results: In this report it is shown that the glnA1 and glnA2 encoded glutamine synthetase sequences were inherited from an Actinobacteria ancestor, while the glnA4 and glnA3 encoded GS sequences were sequentially acquired during Actinobacteria speciation. The glutamine synthetase sequences encoded by glnA4 and glnA3 are undergoing reductive evolution in the mycobacteria, whilst those encoded by glnA1 and glnA2 are more conserved.

Conclusion: Different selective pressures by the ecological niche that the organisms occupy may influence the sequence evolution of glnA1 and glnA2 and thereby affecting phylogenies based on the protein sequences they encode. The findings in this report may impact the use of similar sequences as molecular markers, as well as shed some light on the evolution of glutamine synthetase in the mycobacteria.

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Phylogenetic analysis of the all the actinobacterial glnA protein sequences showed that the glnA3 and glnA4 protein sequences are closer related to the glnA2 protein sequence that to that of glnA1. (Distances not drawn to scale).
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Figure 3: Phylogenetic analysis of the all the actinobacterial glnA protein sequences showed that the glnA3 and glnA4 protein sequences are closer related to the glnA2 protein sequence that to that of glnA1. (Distances not drawn to scale).

Mentions: The sequence annotations of the M. tuberculosis glnA genes suggest that glnA1 and glnA3 encode GSI enzymes and glnA2 and glnA4 GSII enzymes, which together with the results summarised in Figure 1, suggest that the glnA4 and glnA3 GS sequences were acquired either through sequential duplication of a GSI and GSII sequence, or through separate lateral genetic transfer events. Therefore the ancestry of the glnA sequences was investigated through a phylogenetic analysis of all the glnA sequences present in the phylum Actinobacteria (Table 1). The simplified tree shown in Figure 3 (see additional file 1) indicates that, consistent with previous reports, the glnA-encoded protein sequences may have been derived from a common ancestral GS sequence [4]. The sequence phylogeny further shows that the glnA2, glnA3 and glnA4-encoded sequences are clustered on a separate branch from the glnA1-encoded sequence, indicating that these sequence are related and may share a common ancestor.


Glutamine synthetase sequence evolution in the mycobacteria and their use as molecular markers for Actinobacteria speciation.

Hayward D, van Helden PD, Wiid IJ - BMC Evol. Biol. (2009)

Phylogenetic analysis of the all the actinobacterial glnA protein sequences showed that the glnA3 and glnA4 protein sequences are closer related to the glnA2 protein sequence that to that of glnA1. (Distances not drawn to scale).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2667176&req=5

Figure 3: Phylogenetic analysis of the all the actinobacterial glnA protein sequences showed that the glnA3 and glnA4 protein sequences are closer related to the glnA2 protein sequence that to that of glnA1. (Distances not drawn to scale).
Mentions: The sequence annotations of the M. tuberculosis glnA genes suggest that glnA1 and glnA3 encode GSI enzymes and glnA2 and glnA4 GSII enzymes, which together with the results summarised in Figure 1, suggest that the glnA4 and glnA3 GS sequences were acquired either through sequential duplication of a GSI and GSII sequence, or through separate lateral genetic transfer events. Therefore the ancestry of the glnA sequences was investigated through a phylogenetic analysis of all the glnA sequences present in the phylum Actinobacteria (Table 1). The simplified tree shown in Figure 3 (see additional file 1) indicates that, consistent with previous reports, the glnA-encoded protein sequences may have been derived from a common ancestral GS sequence [4]. The sequence phylogeny further shows that the glnA2, glnA3 and glnA4-encoded sequences are clustered on a separate branch from the glnA1-encoded sequence, indicating that these sequence are related and may share a common ancestor.

Bottom Line: Intriguingly, previous reports have shown that only one copy (glnA1) is essential for growth in M. tuberculosis, while the other copies (glnA2, glnA3 and glnA4) are not.In this report it is shown that the glnA1 and glnA2 encoded glutamine synthetase sequences were inherited from an Actinobacteria ancestor, while the glnA4 and glnA3 encoded GS sequences were sequentially acquired during Actinobacteria speciation.Different selective pressures by the ecological niche that the organisms occupy may influence the sequence evolution of glnA1 and glnA2 and thereby affecting phylogenies based on the protein sequences they encode.

View Article: PubMed Central - HTML - PubMed

Affiliation: DST/NRF Centre for Excellence in Biomedical Tuberculosis Research, US/MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Faculty of Health Sciences - Stellenbosch University, South Africa. dh@sun.ac.za

ABSTRACT

Background: Although the gene encoding for glutamine synthetase (glnA) is essential in several organisms, multiple glnA copies have been identified in bacterial genomes such as those of the phylum Actinobacteria, notably the mycobacterial species. Intriguingly, previous reports have shown that only one copy (glnA1) is essential for growth in M. tuberculosis, while the other copies (glnA2, glnA3 and glnA4) are not.

Results: In this report it is shown that the glnA1 and glnA2 encoded glutamine synthetase sequences were inherited from an Actinobacteria ancestor, while the glnA4 and glnA3 encoded GS sequences were sequentially acquired during Actinobacteria speciation. The glutamine synthetase sequences encoded by glnA4 and glnA3 are undergoing reductive evolution in the mycobacteria, whilst those encoded by glnA1 and glnA2 are more conserved.

Conclusion: Different selective pressures by the ecological niche that the organisms occupy may influence the sequence evolution of glnA1 and glnA2 and thereby affecting phylogenies based on the protein sequences they encode. The findings in this report may impact the use of similar sequences as molecular markers, as well as shed some light on the evolution of glutamine synthetase in the mycobacteria.

Show MeSH
Related in: MedlinePlus