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Excision of an unstable pathogenicity island in Salmonella enterica serovar Enteritidis is induced during infection of phagocytic cells.

Quiroz TS, Nieto PA, Tobar HE, Salazar-Echegarai FJ, Lizana RJ, Quezada CP, Santiviago CA, Araya DV, Riedel CA, Kalergis AM, Bueno SM - PLoS ONE (2011)

Bottom Line: Importantly, we also found that one type of excision occurred at higher rates when S.Enteritidis was residing inside murine phagocytic cells.These data suggest that ROD21 is an unstable pathogenicity island, whose frequency of excision depends on the environmental conditions found inside phagocytic cells.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile.

ABSTRACT
The availability of the complete genome sequence of several Salmonella enterica serovars has revealed the presence of unstable genetic elements in these bacteria, such as pathogenicity islands and prophages. This is the case of Salmonella enterica serovar Enteritidis (S. Enteritidis), a bacterium that causes gastroenteritis in humans and systemic infection in mice. The whole genome sequence analysis for S. Enteritidis unveiled the presence of several genetic regions that are absent in other Salmonella serovars. These regions have been denominated "regions of difference" (ROD). In this study we show that ROD21, one of such regions, behaves as an unstable pathogenicity island. We observed that ROD21 undergoes spontaneous excision by two independent recombination events, either under laboratory growth conditions or during infection of murine cells. Importantly, we also found that one type of excision occurred at higher rates when S. Enteritidis was residing inside murine phagocytic cells. These data suggest that ROD21 is an unstable pathogenicity island, whose frequency of excision depends on the environmental conditions found inside phagocytic cells.

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Schematic representation of excisions type 1 and type 2 of ROD21 and the respective episomal elements generated.(A) Schematic representation of ROD21 and its surrounding region in the chromosome of the S. Enteritidis NCTC13349 strain. Light gray arrows indicate genes that are part of ROD21, black arrows indicate neighboring genes located outside ROD21 and dark gray arrows show neighboring genes specifically contained between the DRS limiting ROD21 and the asnT-3 gene. Portions of the chromosome involved in type 1 and 2 excisions are shown by connecting the respective recombining DRS/tRNAs (dotted lines). Numbered arrows indicate the regions where the primers used in this study hybridize. (B) Schematic representation of the attB-1 and attP-1 sites formed after type 1 excision and the genes remaining in both the chromosome of S. Enteritidis and the episomal element. (C) Schematic representation of the attB-2 and attP-2 sites formed after type 2 excision, and the genes remaining in both the chromosome of S. Enteritidis and in the episomal element. Primer pairs used to detect the chromosomal excisions and episomal elements are indicated as black arrows.
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pone-0026031-g002: Schematic representation of excisions type 1 and type 2 of ROD21 and the respective episomal elements generated.(A) Schematic representation of ROD21 and its surrounding region in the chromosome of the S. Enteritidis NCTC13349 strain. Light gray arrows indicate genes that are part of ROD21, black arrows indicate neighboring genes located outside ROD21 and dark gray arrows show neighboring genes specifically contained between the DRS limiting ROD21 and the asnT-3 gene. Portions of the chromosome involved in type 1 and 2 excisions are shown by connecting the respective recombining DRS/tRNAs (dotted lines). Numbered arrows indicate the regions where the primers used in this study hybridize. (B) Schematic representation of the attB-1 and attP-1 sites formed after type 1 excision and the genes remaining in both the chromosome of S. Enteritidis and the episomal element. (C) Schematic representation of the attB-2 and attP-2 sites formed after type 2 excision, and the genes remaining in both the chromosome of S. Enteritidis and in the episomal element. Primer pairs used to detect the chromosomal excisions and episomal elements are indicated as black arrows.

Mentions: Next, we tested whether ROD21 is able to undergo spontaneous excision from the bacterial chromosome. Because ROD21 is flanked by three copies of asnT and delimited by the DRS, at least two types of recombination events may take place: recombination between asnT-2 and the DRS (excision type 1) and recombination between asnT-2 and asnT-3 (excision type 2). Either one of these recombination events might result in the complete excision of this new pathogenicity island (Fig. 2).


Excision of an unstable pathogenicity island in Salmonella enterica serovar Enteritidis is induced during infection of phagocytic cells.

Quiroz TS, Nieto PA, Tobar HE, Salazar-Echegarai FJ, Lizana RJ, Quezada CP, Santiviago CA, Araya DV, Riedel CA, Kalergis AM, Bueno SM - PLoS ONE (2011)

Schematic representation of excisions type 1 and type 2 of ROD21 and the respective episomal elements generated.(A) Schematic representation of ROD21 and its surrounding region in the chromosome of the S. Enteritidis NCTC13349 strain. Light gray arrows indicate genes that are part of ROD21, black arrows indicate neighboring genes located outside ROD21 and dark gray arrows show neighboring genes specifically contained between the DRS limiting ROD21 and the asnT-3 gene. Portions of the chromosome involved in type 1 and 2 excisions are shown by connecting the respective recombining DRS/tRNAs (dotted lines). Numbered arrows indicate the regions where the primers used in this study hybridize. (B) Schematic representation of the attB-1 and attP-1 sites formed after type 1 excision and the genes remaining in both the chromosome of S. Enteritidis and the episomal element. (C) Schematic representation of the attB-2 and attP-2 sites formed after type 2 excision, and the genes remaining in both the chromosome of S. Enteritidis and in the episomal element. Primer pairs used to detect the chromosomal excisions and episomal elements are indicated as black arrows.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198454&req=5

pone-0026031-g002: Schematic representation of excisions type 1 and type 2 of ROD21 and the respective episomal elements generated.(A) Schematic representation of ROD21 and its surrounding region in the chromosome of the S. Enteritidis NCTC13349 strain. Light gray arrows indicate genes that are part of ROD21, black arrows indicate neighboring genes located outside ROD21 and dark gray arrows show neighboring genes specifically contained between the DRS limiting ROD21 and the asnT-3 gene. Portions of the chromosome involved in type 1 and 2 excisions are shown by connecting the respective recombining DRS/tRNAs (dotted lines). Numbered arrows indicate the regions where the primers used in this study hybridize. (B) Schematic representation of the attB-1 and attP-1 sites formed after type 1 excision and the genes remaining in both the chromosome of S. Enteritidis and the episomal element. (C) Schematic representation of the attB-2 and attP-2 sites formed after type 2 excision, and the genes remaining in both the chromosome of S. Enteritidis and in the episomal element. Primer pairs used to detect the chromosomal excisions and episomal elements are indicated as black arrows.
Mentions: Next, we tested whether ROD21 is able to undergo spontaneous excision from the bacterial chromosome. Because ROD21 is flanked by three copies of asnT and delimited by the DRS, at least two types of recombination events may take place: recombination between asnT-2 and the DRS (excision type 1) and recombination between asnT-2 and asnT-3 (excision type 2). Either one of these recombination events might result in the complete excision of this new pathogenicity island (Fig. 2).

Bottom Line: Importantly, we also found that one type of excision occurred at higher rates when S.Enteritidis was residing inside murine phagocytic cells.These data suggest that ROD21 is an unstable pathogenicity island, whose frequency of excision depends on the environmental conditions found inside phagocytic cells.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile.

ABSTRACT
The availability of the complete genome sequence of several Salmonella enterica serovars has revealed the presence of unstable genetic elements in these bacteria, such as pathogenicity islands and prophages. This is the case of Salmonella enterica serovar Enteritidis (S. Enteritidis), a bacterium that causes gastroenteritis in humans and systemic infection in mice. The whole genome sequence analysis for S. Enteritidis unveiled the presence of several genetic regions that are absent in other Salmonella serovars. These regions have been denominated "regions of difference" (ROD). In this study we show that ROD21, one of such regions, behaves as an unstable pathogenicity island. We observed that ROD21 undergoes spontaneous excision by two independent recombination events, either under laboratory growth conditions or during infection of murine cells. Importantly, we also found that one type of excision occurred at higher rates when S. Enteritidis was residing inside murine phagocytic cells. These data suggest that ROD21 is an unstable pathogenicity island, whose frequency of excision depends on the environmental conditions found inside phagocytic cells.

Show MeSH
Related in: MedlinePlus