Characterization of microsporidian Ameson herrnkindi sp. nov. infecting Caribbean spiny lobsters Panulirus argus

Microsporidia Ameson earli sp. n. and A. michaelis (Sprague 1965) infecting blue crabs Callinectes sapidus from shedding facilities in Louisiana

During a survey for pathogens and commensals of blue crabs in commercial soft shell shedding facilities in Louisiana, we discovered an occurrence of microsporidiosis in two of forty examined crabs. Judging from spore shape and size, tissue tropism and external signs of muscle pathology, the causative agent of infections was identified as Ameson michaelis, a muscle-infecting species that has been repeatedly detected in populations of Callinectes sapidus in Louisiana since 1965. However, retrospective ultrastructural examination revealed that in one of Ameson-infected crabs, infection was caused by a parasite with ultrastructural characters not completely compliant with the ones of A. michaelis. The major difference was the absence of microtubule-like appendages attached to the exospore, typical of A. michaelis and other Ameson spp. SSUrDNA-inferred pairwise evolutionary distances between the novel species and other Ameson spp. ranged from 0.006 to 0.051; it was 0.039 in the case of A. michaelis. Hence, we describe here a new species in the genus Ameson, and name it after Prof. Earl Weidner, our colleague and friend, an outstanding microsporidiologist and the author of pioneer papers on the ultrastructure and physiology of A. michaelis.

Microsporidian Pathogens of Aquatic Animals

Around 57.1% of microsporidia occupy aquatic environments, excluding a further 25.7% that utilise both terrestrial and aquatic systems. The aquatic microsporidia therefore compose the most diverse elements of the Microsporidia phylum, boasting unique structural features, variable transmission pathways, and significant ecological influence. From deep oceans to tropical rivers, these parasites are present in most aquatic environments and have been shown to infect hosts from across the Protozoa and Animalia. The consequences of infection range from mortality to intricate behavioural change, and their presence in aquatic communities often alters the overall functioning of the ecosystem.In this chapter, we explore aquatic microsporidian diversity from the perspective of aquatic animal health. Examples of microsporidian parasitism of importance to an aquacultural ('One Health') context and ecosystem context are focussed upon. These include infection of commercially important penaeid shrimp by Enterocytozoon hepatopenaei and interesting hyperparasitic microsporidians of wild host groups.Out of ~1500 suggested microsporidian species, 202 have been adequately taxonomically described using a combination of ultrastructural and genetic techniques from aquatic and semi-aquatic hosts. These species are our primary focus, and we suggest that the remaining diversity have additional genetic or morphological data collected to formalise their underlying systematics.

Morphological and phylogenetic characterization of a new microsporidium, Triwangia gracilipes n. sp. From the freshwater shrimp Caridina gracilipes (Decapoda: Atyidae) in China

A new microsporidian species was described from the freshwater shrimp Caridina gracilipes collected from Lake Luoma located in Northern Jiangsu province, East China. The infected shrimps appeared generally opaque due to the presence of white cysts located in the connective tissues of the surface of the hepatopancreas. The earliest developmental stages observed were diplokaryotic meronts which were in direct contact with the host cell cytoplasm. Multinucleate sporogonial plasmodia developed into uninucleate sporoblasts which were enclosed in sporophorous vesicles. The parasite developed synchronously within an individual sporophorous vesicle. Mature spores were pyriform and monokaryotic, measuring 5.45 ± 0.18 (5.12-5.82) µm long and 3.57 ± 0.17 (3.18-3.92) µm wide. Anisofilar polar filaments coiled 10-12 turns and arranged in one row. Phylogenetic analysis based on the obtained SSU rDNA sequence indicated that the present species clustered with Triwangia caridina with high support value to form an independent branch which was placed at the basal position of a large clade of containing microsporidia of fishes, crustaceans and amphipods. Based on the morphological characters and ultrastructural features, as well as SSU rDNA-inferred phylogenetic relationships, a new species was erected and named as Triwangia gracilipes n. sp. The taxonomic affiliation of Triwangia was also primarily explored.

A novel dimorphic microsporidian Ameson iseebi sp. nov. infecting muscle of the Japanese spiny lobster, Panulirus japonicus, in western Japan

Japanese spiny lobsters (Panulirus japonicus) exhibiting white opaque abdominal muscle were found in Mie and Wakayama prefectures, in mid-Western Japan. Microscopically, two types of microsporidian spores, ovoid and rod-shaped, were observed infecting the muscle. Histologically, both types of spore were detected inside myofibers of the abdomen, appendages, and cardiac muscles and were often both observed in a single myofiber simultaneously. Transmission electron microscopy revealed that ovoid spores have villous projections on the surface, and that ovoid and rod-shaped spores have a polar filament with 12 coils and 6 to 8 coils respectively. Merogonic and sporogonic stages were observed around ovoid spores, but rarely around rod-shaped spores. The small subunit ribosomal DNA sequences obtained from both spore types were identical to each other, indicating that this microsporidian exhibits a clear spore dimorphism. Phylogenetic analysis based on the rDNA sequences indicates that this microsporidian is part of a clade consisting of the genera Ameson and Nadelspora, with the most closely related species being A. herrnkindi found in the Caribbean spiny lobster P. argus. Based on ultrastructural features, molecular phylogenetic data, host type and geographical differences among known species in these genera, the species found in whitened abdominal muscles of the Japanese spiny lobster is described as Ameson iseebi sp. nov.

Post-mortem examination of the Caribbean spiny lobster (Panulirus argus, Latreille 1804) and pathology in a fishery of the Lesser Antilles

The Caribbean spiny lobster, Panulirus argus (Latreille, 1804) is a highly commercial species and comprises the largest spiny lobster fishery in the world. Although populations have declined throughout its range, there is little known regarding its diseases and pathogens. The objectives of this study were to provide illustrated and standardized methods for postmortem examination, and to describe baseline gross and microscopic pathology for P. argus. From July 2017-March 2019, a postmortem examination including comprehensive histological assessment was performed on 313 fishery-caught lobsters. Epibionts and lesions observed include branchial cirriped infestation (69%), branchial encysted nemertean worm larvae (23%), tail fan necrosis (11%), skeletal muscle necrosis (7%), antennal gland calculi (6%), branchial infarction (2%), and microsporidiosis (0.6%). This report confirms the rare prevalence of microsporidiosis in P. argus and describes nemertean worm larvae in the gill. This study also reports a condition resembling excretory calcinosis in spiny lobster. The methods and data produced by this study facilitate disease diagnosis and sustainable stock management of P. argus.

Microsporidia Can Acquire Lamin-like Intermediate Filaments and Cell Adhesion Catenin-cadherin Complexes from the Host (?)

On their spore surfaces, Microsporidia often develop a canopy of filaments with characteristics of intermediate filaments (IF), as we demonstrated in previous studies on Thelohania sp., Ameson michaelis, and Spraguea lophii. Genomic studies indicate that among invertebrates, lamins that may localize in the cytoplasm or nucleus, are the only known IF type. These IFs can bind to the substrate containing cell adhesion molecules (CAMs) cadherins, associated with β and γ catenins. The objects of this study were to determine whether microsporidia have CAMs with the attached IFs on their envelopes and to find out if these proteins are provided by the host. An examination was made for localization of lamins and CAMs on the spores of the mentioned above species and Anncaliia algerae, plus in the host animals. Then, we determined whether the spores of A. michaelis and A. algerae could bind vertebrate nuclear lamin onto the spore surface. We also tested transgenic Drosophila melanogaster stocks bearing cadherin-GFP to see whether developing A. algerae parasites in these hosts could acquire host CAMs. The tests were positive for all these experiments. We hypothesize that microsporidia are able to acquire host lamin IFs and cell adhesion catenin-cadherin complexes from the host.