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Journal of Bacteriology, October 2006, p. 7176-7185, Vol. 188, No. 20
0021-9193/06/$08.00+0     doi:10.1128/JB.01021-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Positive Selection on Transposase Genes of Insertion Sequences in the Crocosphaera watsonii Genome{dagger} ,{ddagger}

Ted H. M. Mes* and Marije Doeleman

Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, POB 140, 4400 AC Yerseke, The Netherlands

Received 12 July 2006/ Accepted 1 August 2006

Insertion sequences (ISs) are mobile elements that are commonly found in bacterial genomes. Here, the structural and functional diversity of these mobile elements in the genome of the cyanobacterium Crocosphaera watsonii WH8501 is analyzed. The number, distribution, and diversity of nucleotide and amino acid stretches with similarity to the transposase gene of this IS family suggested that this genome harbors many functional as well as truncated IS fragments. The selection pressure acting on full-length transposase open reading frames of these ISs suggested (i) the occurrence of positive selection and (ii) the presence of one or more positively selected codons. These results were obtained using three data sets of transposase genes from the same IS family that were collected based on the level of amino acid similarity, the presence of an inverted repeat, and the number of sequences in the data sets. Neither recombination nor ribosomal frameshifting, which may interfere with the selection analyses, appeared to be important forces in the transposase gene family. Some positively selected codons were located in a conserved domain, suggesting that these residues are functionally important. The finding that this type of selection acts on IS-carried genes is intriguing, because although ISs have been associated with the adaptation of the bacterial host to new environments, this has typically been attributed to transposition or transformation, thus involving different genomic locations. Intragenic adaptation of IS-carried genes identified here may constitute a novel mechanism associated with bacterial diversification and adaptation.

* Corresponding author. Mailing address: Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, POB 140, 4400 AC Yerseke, The Netherlands. Phone: 31-113577482. Fax: 31-113573616. E-mail: t.mes{at}nioo.knaw.nl.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Publication 3896 of NIOO-KNAW.

Journal of Bacteriology, October 2006, p. 7176-7185, Vol. 188, No. 20
0021-9193/06/$08.00+0     doi:10.1128/JB.01021-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Zehr, J. P., Bench, S. R., Mondragon, E. A., McCarren, J., DeLong, E. F. (2007). Low genomic diversity in tropical oceanic N2-fixing cyanobacteria. Proc. Natl. Acad. Sci. USA 104: 17807-17812 [Abstract] [Full Text]  


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