Genetic signature analysis of Perkinsus marinus in Mexico suggests possible translocation from the Atlantic Ocean to the Pacific coast of Mexico

A qPCR-Based Survey of Haplosporidium nelsoni and Perkinsus spp. in the Eastern Oyster, Crassostrea virginica in Maine, USA

Eastern oyster (Crassostrea virginica) aquaculture is increasingly playing a significant role in the state of Maine's (USA) coastal economy. Here, we conducted a qPCR-based survey for Haplosporidium nelsoni, Perkinsus marinus, and Perkinsus chesapeaki in C. virginica (n = 1440) from six Maine sites during the summer-fall of 2016 and 2017. In the absence of reported die-offs, our results indicated the continued presence of the three protozoan parasites in the six sites. The highest H. nelsoni qPCR-prevalence corresponded to Jack's Point and Prentiss Island (x=40 and 48% respectively), both located in the Damariscotta River Estuary. Jack's Point, Prentiss Island, New Meadows River, and Weskeag River recorded the highest qPCR-prevalence for P. marinus (32-39%). While the P. marinus qPCR-prevalence differed slightly for the years 2016 and 2017, P. chesapeaki qPCR-prevalence in 2016 was markedly lower than 2017 (<20% at all sites versus >60% at all sites for each of the years, respectively). Mean qPCR-prevalence values for P. chesapeaki over the two-year study were ≥40% for samples from Jack's Point (49%), Prentiss Island (44%), and New Meadows River (40%). This study highlights that large and sustained surveys for parasitic diseases are fundamental for decision making toward the management of the shellfish aquaculture industry, especially for having a baseline in the case that die-offs occur.

Detection of haplosporidian protistan parasites supports an increase to their known diversity, geographic range and bivalve host specificity

Haplosporidian protist parasites are a major concern for aquatic animal health, as they have been responsible for some of the most significant marine epizootics on record. Despite their impact on food security, aquaculture and ecosystem health, characterizing haplosporidian diversity, distributions and host range remains challenging. In this study, water filtering bivalve species, cockles Cerastoderma edule, mussels Mytilus spp. and Pacific oysters Crassostrea gigas, were screened using molecular genetic assays using deoxyribonucleic acid (DNA) markers for the Haplosporidia small subunit ribosomal deoxyribonucleic acid region. Two Haplosporidia species, both belonging to the Minchinia clade, were detected in C. edule and in the blue mussel Mytilus edulis in a new geographic range for the first time. No haplosporidians were detected in the C. gigas, Mediterranean mussel Mytilus galloprovincialis or Mytilus hybrids. These findings indicate that host selection and partitioning are occurring amongst cohabiting bivalve species. The detection of these Haplosporidia spp. raises questions as to whether they were always present, were introduced unintentionally via aquaculture and or shipping or were naturally introduced via water currents. These findings support an increase in the known diversity of a significant parasite group and highlight that parasite species may be present in marine environments but remain undetected, even in well-studied host species.

Puromycin selection for stable transfectants of the oyster-infecting parasite Perkinsus marinus

Perkinsus marinus is a marine protozoan parasite that infects natural and farmed oysters, attracting attention from researchers in both fisheries and evolutionary biology. The functions of almost all cellular components and organelles are, however, poorly understood even though a draft genome sequence of P. marinus is publicly available. One of the major obstacles for a functional study of the parasite is limited experimental means for genetic manipulation: a transfection method was established in 2008, and the first drug selection system with bleomycin was reported in 2016. We here introduce the second drug-selectable marker for selection of P. marinus transfectants. The parasite growth is efficiently inhibited by puromycin (IC₅₀ = 4.96 μg/mL), and transfection of its resistance gene, puromycin-N-acetyl-transferase (pac), confers resistance to the drug on the parasite. Stable transfectants can be obtained within 2 months by treating with puromycin at 100 μg/mL. Furthermore, combining puromycin and bleomycin treatment can select transfectants co-expressing two marker genes. This dual-transfection method raises the possibility of using co-localization to identify the cellular localization of novel proteins in P. marinus, thereby contributing to the understanding of cellular functions and pathogenesis.