The quahog parasite unknown, or QPX, is a single-celled protist parasite in the class Labyrinthulomycota that affects hard clams (Mercenaria mercenaria; quahogs),[1] both cultured and wild.[2]
Parasites similar to QPX were first observed in New Brunswick, Canada, in 1959, when a mass death of hard clams was observed. Outbreaks have also occurred in Nova Scotia, Prince Edward Island, New York, New Jersey, Massachusetts, and Virginia, always only in quahog clams.[1][3]
Symptoms of QPX include chipping of the shells, mantle swelling, stunted shell growth and the development of nodules.[3][2]
Biology edit
The life stages of thalli, endospores, and sporangia have been observed.[3] It somewhat resembles the unrelated protist haplosporidian parasite Haplosporidium nelsoni (MPX), a pathogen of the eastern oyster.[2]
QPX was originally considered a chytrid, but has now been provisionally assigned to the phylum Labyrinthulomycota in either the families Thraustochytriidae or Labyrinthulidae, based on the organism having a "uninucleate biflagellate zoospore stage, a loose multilaminar cell wall, and particularly an intracellular sagenogen-like structure".[4] However, much about it is still unknown.[1] QPX-like organisms also may not be all of the same species.[2]
Molecular phylogenetic on the SSU rRNA of QPX was able to produce the same phylum-level identification, and more precisely down to the family Thraustochytriidae next to Thraustochytrium pachydermum. A PCR primer targeting this region that detects QPX infection has been constructed.[5]
QPX can be cultured in laboratories, with the optimal temperature being 20 to 23 °C. It produces a mucus that causes inflammation in the clam and shields itself from clam immune response.[6]
Control and epidemiology edit
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Genetics edit
The partial genome of QPX has been sequenced by the shotgun method in 2013, along with the transcriptome to identify genes important in stress response (mainly temperature). A few interesting proteins and a wide range of genetic polymorphisms have been identified. It expresses some genes involved in the synthesis of antibiotics that are also toxic to clams.[6] Further experimental characterisation in 2018 of these single-nucleotide polymorphisms shows variations in genes related to virulence and environmental (salinity and temperature) adaptation.[7]
References edit
- ^ a b c Ragone Calvo, L.M.; Walker, J.G.; Burreson, E.M. (Jul 30, 1998). "Prevalence and distribution of QPX, Quahog Parasite Unknown, in hard clams Mercenaria mercenaria in Virginia, USA" (PDF). Diseases of Aquatic Organisms. 33 (3): 209–19. doi:10.3354/dao033209. PMID 9745718.
- ^ a b c d Coen, Loren; Bobo, M. Yvonne; Richardson, Donnia; Anderson, Willam D. "Sheet for QPX (Quahog Parasite Unknown)" (PDF). Retrieved 3 January 2017.
- ^ a b c "QPX Disease in Hard Clams" (PDF). Sea Grant New York. Retrieved 30 October 2016.
- ^ Ragan, Mark A.; MacCallum, Greg S.; Murphy, Colleen A.; Cannone, Jamie J.; Gutell, Robin R.; McGladdery, Sharon E. (28 September 2000). "Protistan parasite QPX of hard-shell clam Mercenaria mercenaria is a member of Labyrinthulomycota" (PDF). Diseases of Aquatic Organisms. 42 (3): 185–90. doi:10.3354/dao042185. PMID 11104069. Retrieved 31 October 2016.
- ^ Stokes, NA; Ragone Calvo, LM; Reece, KS; Burreson, EM (2002). "Molecular diagnostics, field validation, and phylogenetic analysis of Quahog Parasite Unknown (QPX), a pathogen of the hard clam Mercenaria mercenaria". Diseases of Aquatic Organisms. 52 (3): 233–247. doi:10.3354/dao052233. PMID 12553451.
- ^ a b Garcia-Vedrenne, Ana Elisa; Groner, Maya; Page-Karjian, Annie; Siegmund, Gregor-Fausto; Singhal, Sonia; Sziklay, Jamie; Roberts, Steven; Benos, Panayiotis V. (17 September 2013). "Development of Genomic Resources for a thraustochytrid Pathogen and Investigation of Temperature Influences on Gene Expression". PLOS ONE. 8 (9): e74196. Bibcode:2013PLoSO...874196G. doi:10.1371/journal.pone.0074196. PMC 3775781. PMID 24069279.
- ^ Bassim, Sleiman; Allam, Bassem (20 June 2018). "SNP hot-spots in the clam parasite QPX". BMC Genomics. 19 (1): 486. doi:10.1186/s12864-018-4866-8. PMC 6011583. PMID 29925308.