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PLoS Genet. 2016 Jan 20;12(1):e1005796. doi: 10.1371/journal.pgen.1005796. eCollection 2016 Jan.

H-NS Facilitates Sequence Diversification of Horizontally Transferred DNAs during Their Integration in Host Chromosomes.

Author information

1
Department of Biological Information, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan.
2
Department of Biomedical Informatics, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.
3
Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa-shi, Chiba, Japan.
4
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Nara, Japan.
5
Earth-Life Science Institute, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan.

Abstract

Bacteria can acquire new traits through horizontal gene transfer. Inappropriate expression of transferred genes, however, can disrupt the physiology of the host bacteria. To reduce this risk, Escherichia coli expresses the nucleoid-associated protein, H-NS, which preferentially binds to horizontally transferred genes to control their expression. Once expression is optimized, the horizontally transferred genes may actually contribute to E. coli survival in new habitats. Therefore, we investigated whether and how H-NS contributes to this optimization process. A comparison of H-NS binding profiles on common chromosomal segments of three E. coli strains belonging to different phylogenetic groups indicated that the positions of H-NS-bound regions have been conserved in E. coli strains. The sequences of the H-NS-bound regions appear to have diverged more so than H-NS-unbound regions only when H-NS-bound regions are located upstream or in coding regions of genes. Because these regions generally contain regulatory elements for gene expression, sequence divergence in these regions may be associated with alteration of gene expression. Indeed, nucleotide substitutions in H-NS-bound regions of the ybdO promoter and coding regions have diversified the potential for H-NS-independent negative regulation among E. coli strains. The ybdO expression in these strains was still negatively regulated by H-NS, which reduced the effect of H-NS-independent regulation under normal growth conditions. Hence, we propose that, during E. coli evolution, the conservation of H-NS binding sites resulted in the diversification of the regulation of horizontally transferred genes, which may have facilitated E. coli adaptation to new ecological niches.

PMID:
26789284
PMCID:
PMC4720273
DOI:
10.1371/journal.pgen.1005796
[Indexed for MEDLINE]
Free PMC Article

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