Erection of a New Genus and Species for the Pathogen of Hard Clams ‘Quahog Parasite Unknown’ (QPX): Mucochytrium quahogii gen. nov., sp. nov.

Mucochytrium quahogii (=QPX) Is a Commensal, Opportunistic Pathogen of the Hard Clam (Mercenaria mercenaria): Evidence and Implications for QPX Disease Management

“…In contrast, M. quahogii did not exhibit these relationships, despite known effects of salinity on M. quahogii in vitro. In culture, growth by endosporulation [37,38] and zoosporulation [1] has an inverse relationship with salinity with suppression observed at lower salinities; however, differences in salinity among sites did not seem to be related to M. quahogii abundance in this study.…”

“…Mucochytrium quahogii, commonly known as Quahog Parasite Unknown (QPX), is the causative agent of QPX disease in hard clams, Mercenaria mercenaria [1]. M. quahogii belongs to a diverse and ubiquitous group of marine protistan decomposers known as labyrinthulomycetes that are generally nonpathogenic but some of which have been reported as opportunistic pathogens of diverse marine animals [2][3][4].…”

Keeping up with advances in qPCR pathogen detection: an example for QPX disease in hard clams

“…There was a direct relationship between QPX cell diameter and number of DAPI-stained nuclei (cell diameter μm = 0.991 (no. of nuclei) + 4.457, R 2 = 0.753) (Geraci-Yee et al 2021). The average cell diameter and number of nuclei of the < 5 μm fraction cells were 3.5 μm and 1.3 nuclei, compared to 9.6 μm and 6 nuclei in the > 5 μm fraction.…”

“…The DNA content of QPX cells was determined by Liu et al (2009) in order to convert QPX copy number to QPX cell number (Galluzzi et al 2004), assuming that the rDNA copy number of QPX cells in culture is similar to that of QPX in clams. Since QPX cells in clam tissue and in culture usually contain multiple nuclei, varying with cell size and life stage (Geraci-Yee 2021, Geraci-Yee et al 2021), this procedure was repeated with the addition of a DAPI (4',6-diamidino-2-phenylindole) staining step to determine DNA content per nucleus using a geographically representative mixture of 4 QPX isolates, 2 from New York (8BC7 = ATCC TSD-50 and 20AC1), 1 from Massachusetts (MA; ATCC 50749), and 1 from Virginia (VA) (Geraci-Yee et al 2021). The 4 QPX isolates were individually cultured in modified minimal essential medium (MEM) supplemented with 10% fetal bovine serum (FBS) (Kleinschuster et al 1998) or ATCC medium 2126, at room temperature on an orbital shaker at low speed to reduce mucus pro-duction.…”

“…Disease management practices suitable for most marine organisms are limited to reducing pathogen impact and inputs, which requires extensive knowledge on pathogen biology and ecology (Harvell et al 2004, McCallum et al 2004, Renault 2008, Burge et al 2014. One example is the pathogen of the hard clam Mercenaria mercenaria, long known as Quahog Parasite Unknown (QPX) and recently described formally as Mucochytrium quahogii Geraci-Yee & Allam, 2021 (Geraci-Yee et al 2021). QPX can cause severe mortality events in hard clams, and although all evidence to date suggests that QPX is an opportunistic pathogen (Ford et al 2002, Burge et al 2013, Geraci-Yee 2021, many aspects of the disease and the QPX organism (M. quahogii) remain too poorly understood to confirm this theory or influence resource management decisions.…”