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Plasmid composition in Aeromonas salmonicida subsp. salmonicida 01-B526 unravels unsuspected type three secretion system loss patterns.

Abstract：

BACKGROUND:Aeromonas salmonicida subsp. salmonicida is a ubiquitous psychrophilic waterborne bacterium and a fish pathogen. The numerous mobile elements, especially insertion sequences (IS), in its genome promote rearrangements that impact its phenotype. One of the main virulence factors of this bacterium, its type three secretion system (TTSS), is affected by these rearrangements. In Aeromonas salmonicida subsp. salmonicida most of the TTSS genes are encoded in a single locus on a large plasmid called pAsa5, and may be lost when the bacterium is cultivated at a higher temperature (25 °C), producing non-virulent mutants. In a previous study, pAsa5-rearranged strains that lacked the TTSS locus on pAsa5 were produced using parental strains, including 01-B526. Some of the generated deletions were explained by homologous recombination between ISs found on pAsa5, whereas the others remained unresolved. To investigate those rearrangements, short- and long-read high-throughput sequencing technologies were used on the A. salmonicida subsp. salmonicida 01-B526 whole genome. RESULTS:Whole genome sequencing of the 01-B526 strain revealed that its pAsa5 has an additional IS copy, an ISAS5, compared to the reference strain (A449) sequence, which allowed for a previously unknown rearrangement to occur. It also appeared that 01-B526 bears a second large plasmid, named pAsa9, which shares 40 kbp of highly similar sequences with pAsa5. Following these discoveries, previously unexplained deletions were elucidated by genotyping. Furthermore, in one of the derived strains a fusion of pAsa5 and pAsa9, involving the newly discovered ISAS5 copy, was observed. CONCLUSION:The loss of TTSS and hence virulence is explained by one consistent mechanism: IS-driven homologous recombination. The similarities between pAsa9 and pAsa5 also provide another example of genetic diversity driven by ISs.

journal_name

BMC Genomics

journal_title

BMC genomics

authors

Tanaka KH,Vincent AT,Emond-Rheault JG,Adamczuk M,Frenette M,Charette SJ

doi

10.1186/s12864-017-3921-1

subject

Has Abstract

pub_date

2017-07-12 00:00:00

pages

528

issue

issn

1471-2164

pii

10.1186/s12864-017-3921-1

journal_volume

pub_type

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Plasmid composition in Aeromonas salmonicida subsp. salmonicida 01-B526 unravels unsuspected type three secretion system loss patterns.