A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i>
The marine bacterium <i>Photobacterium damselae</i> subsp. <i>piscicida</i> (<i>Pdp</i>) causes photobacteriosis in fish and important financial losses in aquaculture, but knowledge of its virulence factors is still scarce. We here demonstrate that an unstable pla...
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MDPI AG
2022-04-01
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| Series: | International Journal of Molecular Sciences |
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| Online Access: | https://www.mdpi.com/1422-0067/23/9/4729 |
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| author | Saqr Abushattal Ana Vences Carlos R. Osorio |
| author_facet | Saqr Abushattal Ana Vences Carlos R. Osorio |
| author_sort | Saqr Abushattal |
| collection | DOAJ |
| description | The marine bacterium <i>Photobacterium damselae</i> subsp. <i>piscicida</i> (<i>Pdp</i>) causes photobacteriosis in fish and important financial losses in aquaculture, but knowledge of its virulence factors is still scarce. We here demonstrate that an unstable plasmid (pPHDPT3) that encodes a type III secretion system (T3SS) is highly prevalent in <i>Pdp</i> strains from different geographical origins and fish host species. We found that pPHDPT3 undergoes curing upon in vitro cultivation, and this instability constitutes a generalized feature of pPHDPT3-like plasmids in <i>Pdp</i> strains. pPHDPT3 markers were detected in tissues of naturally-infected moribund fish and in the <i>Pdp</i> colonies grown directly from the fish tissues but were undetectable in a fraction of the colonies produced upon the first passage of the primeval colonies on agar plates. Notably, cured strains exhibited a marked reduction in virulence for fish, demonstrating that pPHDPT3 is a major virulence factor of <i>Pdp</i>. The attempts to stabilize pPHDPT3 by insertion of antibiotic resistance markers by allelic exchange caused an even greater reduction in virulence. We hypothesize that the existence of a high pressure to shed pPHDPT3 plasmid in vitro caused the selection of clones with off-target mutations and gene rearrangements during the process of genetic modification. Collectively, these results show that pPHDPT3 constitutes a novel, hitherto unreported virulence factor of <i>Pdp</i> that shows a high instability in vitro and warn that the picture of <i>Pdp</i> virulence genes has been historically underestimated, since the loss of the T3SS and other plasmid-borne genes may have occurred systematically in laboratories for decades. |
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| last_indexed | 2024-03-10T04:06:01Z |
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| series | International Journal of Molecular Sciences |
| spelling | doaj.art-319dddb1ffd84f23ad1e2d4cda07af5e2023-11-23T08:21:28ZengMDPI AGInternational Journal of Molecular Sciences1661-65961422-00672022-04-01239472910.3390/ijms23094729A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i>Saqr Abushattal0Ana Vences1Carlos R. Osorio2Departamento de Microbioloxía e Parasitoloxía, Instituto de Acuicultura, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, SpainDepartamento de Microbioloxía e Parasitoloxía, Instituto de Acuicultura, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, SpainDepartamento de Microbioloxía e Parasitoloxía, Instituto de Acuicultura, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, SpainThe marine bacterium <i>Photobacterium damselae</i> subsp. <i>piscicida</i> (<i>Pdp</i>) causes photobacteriosis in fish and important financial losses in aquaculture, but knowledge of its virulence factors is still scarce. We here demonstrate that an unstable plasmid (pPHDPT3) that encodes a type III secretion system (T3SS) is highly prevalent in <i>Pdp</i> strains from different geographical origins and fish host species. We found that pPHDPT3 undergoes curing upon in vitro cultivation, and this instability constitutes a generalized feature of pPHDPT3-like plasmids in <i>Pdp</i> strains. pPHDPT3 markers were detected in tissues of naturally-infected moribund fish and in the <i>Pdp</i> colonies grown directly from the fish tissues but were undetectable in a fraction of the colonies produced upon the first passage of the primeval colonies on agar plates. Notably, cured strains exhibited a marked reduction in virulence for fish, demonstrating that pPHDPT3 is a major virulence factor of <i>Pdp</i>. The attempts to stabilize pPHDPT3 by insertion of antibiotic resistance markers by allelic exchange caused an even greater reduction in virulence. We hypothesize that the existence of a high pressure to shed pPHDPT3 plasmid in vitro caused the selection of clones with off-target mutations and gene rearrangements during the process of genetic modification. Collectively, these results show that pPHDPT3 constitutes a novel, hitherto unreported virulence factor of <i>Pdp</i> that shows a high instability in vitro and warn that the picture of <i>Pdp</i> virulence genes has been historically underestimated, since the loss of the T3SS and other plasmid-borne genes may have occurred systematically in laboratories for decades.https://www.mdpi.com/1422-0067/23/9/4729<i>Photobacterium damselae</i> subsp. <i>piscicida</i>fish pasteurellosisT3SSplasmidplasmid curing |
| spellingShingle | Saqr Abushattal Ana Vences Carlos R. Osorio A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i> International Journal of Molecular Sciences <i>Photobacterium damselae</i> subsp. <i>piscicida</i> fish pasteurellosis T3SS plasmid plasmid curing |
| title | A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i> |
| title_full | A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i> |
| title_fullStr | A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i> |
| title_full_unstemmed | A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i> |
| title_short | A Highly Unstable and Elusive Plasmid That Encodes the Type III Secretion System Is Necessary for Full Virulence in the Marine Fish Pathogen <i>Photobacterium damselae</i> subsp. <i>piscicida</i> |
| title_sort | highly unstable and elusive plasmid that encodes the type iii secretion system is necessary for full virulence in the marine fish pathogen i photobacterium damselae i subsp i piscicida i |
| topic | <i>Photobacterium damselae</i> subsp. <i>piscicida</i> fish pasteurellosis T3SS plasmid plasmid curing |
| url | https://www.mdpi.com/1422-0067/23/9/4729 |
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