Abstract Background Although the gene encoding for glutamine synthetase (<it>gln</it>A) is essential in several organisms, multiple glnA copies have been identified in bacterial genomes such as those of the phylum <it>Actinobacteria</it>, notably the mycobacterial species. Intriguingly, previous reports have shown that only one copy (<it>gln</it>A1) is essential for growth in <it>M. tuberculosis</it>, while the other copies (<it>gln</it>A2, <it>gln</it>A3 and <it>gln</it>A4) are not. Results In this report it is shown that the <it>gln</it>A1 and <it>gln</it>A2 encoded glutamine synthetase sequences were inherited from an <it>Actinobacteria </it>ancestor, while the <it>gln</it>A4 and <it>gln</it>A3 encoded GS sequences were sequentially acquired during <it>Actinobacteria </it>speciation. The glutamine synthetase sequences encoded by <it>gln</it>A4 and <it>gln</it>A3 are undergoing reductive evolution in the mycobacteria, whilst those encoded by <it>gln</it>A1 and <it>gln</it>A2 are more conserved. Conclusion Different selective pressures by the ecological niche that the organisms occupy may influence the sequence evolution of <it>gln</it>A1 and <it>gln</it>A2 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.</p

Hayward, Don

van Helden, Paul D

Wiid, Ian JF

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