Virulence of Paramoeba invadens Jones (Amoebida, Paramoebidae) from Monoxenic and Polyxenic Culture¹

Abstract

Paramoeba invadens is a pathogenic marine amoeba responsible for mass mortalities of sea urchins (Strongylocentrotus droebachiensis) along the Atlantic coast of Nova Scotia in the early 1980's. The amoeba has been maintained in vivo in S. droebachiensis for five years in the laboratory without observable loss of virulence. Paramoeba invadens was cultured polyxenically (on mixed marine bacteria) and monoxenically (on a single strain of Pseudomonas nautica) on non‐nutrient agar for 58 weeks and 19 weeks respectively. Pathogenicity tests showed some loss of virulence in monoxenic culture after 15 weeks and in polyxenic culture after 58 weeks. Polyxenic culture is recommended for long‐term culture of P. invadens although periodic passage of the amoeba through the sea urchin host may be required to maintain virulence for periods exceeding one year.

Neoparamoeba perurans loses virulence during clonal culture

“…For example, in comparison to mortality rates of controls exposed to Paramoeba invadens maintained in vivo, exposure of sea urchin, Strongylocentrotus droebachiensis, to a 15 week old monoxenic culture of P. invadens did not induce any mortality, while challenge with a 58 week old polyxenic culture of P. invadens delayed mortality of sea urchins by 5 days (Jellett and Scheibling, 1988). Loss of virulence in culture is well documented for isolates of several free-living species of amoebae pathogenic to mammals (Kasprzak et al, 1974).…”

Nuclear Small-Subunit Ribosomal Rna Gene-Based Characterization, Molecular Phylogeny and PCR Detection of the Neoparamoeba From Western Long Island Sound Lobster

“…Efforts to culture the blue crab pathogen have likewise been unsuccessful (Johnson 1977). Cultures of the urchin pathogen were achieved (Jones 1985, Jellett & Scheibling 1988a, Jellett & Scheibling 1988b) but not archived. The only cultures of Paramoeba and Neoparamoeba species available when this study began were of free-living amoebae isolated from water and sediment samples (e.g., Grell 1961, Cann & Page 1982 or from the gills of finfish (e.g., Kent et al 1988).…”

Non-occurrence of free-living Paramoeba invadens in water and sediments of Halifax Harbour, Nova Scotia, Canada

“…Only 2 species in this genus are known to be parasitic (Page 1983, Jones 1985. Paramoeba perniciosa appears to be an obligate parasite (Sprague et al 1969, Page 1983 O Inter-Research/Printed in F. R. Germany from the tissues of diseased sea urchins and their surrounding seawater , but it can be cultured on bacteria and is therefore thought to be a free-living opportunistic parasite (Jones 1985, Jellett & Scheibling 1988b). The only known species of freeliving Paramoeba morphologically similar to P. invadens is P. aestuanna (Page 1983).…”

“…Paramoeba was cultured by placing the filters onto artifical seawater (ASW) agar (Jellett & Scheibling 1988b) in 100 mm disposable plastic petri dishes with ca 20 m1 of ASW overlay (after Page 1983). Cultures were incubated at 15°C for 3 wk in complete darkness.…”

“…There also was no morbidity or mortahty in any individual in either of the control groups. Paramoeba could not b e cultured from radial invadens is known to result after long-term (> 58 tvk) culturing (Jellett & Scheibling 1988b).…”