The genome of the myxosporean Thelohanellus kitauei shows adaptations to nutrient acquisition within its fish host.

Members of Myxozoa, a parasitic metazoan taxon, have considerable detrimental effects on fish hosts and also have been associated with human food-borne illness. Little is known about their biology and metabolism. Analysis of the genome of Thelohanellus kitauei and comparative analysis with genomes of its two free-living cnidarian relatives revealed that T. kitauei has adapted to parasitism, as indicated by the streamlined metabolic repertoire and the tendency toward anabolism rather than catabolism. Thelohanellus kitauei mainly secretes proteases and protease inhibitors for nutrient digestion (parasite invasion), and depends on endocytosis (mainly low-density lipoprotein receptors-mediated type) and secondary carriers for nutrient absorption. Absence of both classic and complementary anaerobic pathways and gluconeogenesis, the lack of de novo synthesis and reduced activity in hydrolysis of fatty acids, amino acids, and nucleotides indicated that T. kitauei in this vertebrate host-parasite system has adapted to inhabit a physiological environment extremely rich in both oxygen and nutrients (especially glucose), which is consistent with its preferred parasitic site, that is, the host gut submucosa. Taking advantage of the genomic and transcriptomic information, 23 potential nutrition-related T. kitauei-specific chemotherapeutic targets were identified. This first genome sequence of a myxozoan will facilitate development of potential therapeutics for efficient control of myxozoan parasites and ultimately prevent myxozoan-induced fish-borne illnesses in humans.

Prevalence and impact of the microsporidium Thelohania solenopsae (Microsporidia) on wild populations of red imported fire ants, Solenopsis invicta, in Louisiana.

We surveyed 165 sites to determine the ecological factors that might influence the distribution and prevalence of Thelohania solenopsae, and its effect on the demography of the red imported fire ant (Solenopsis invicta) in Louisiana. The microsporidium was found in 9.9% of colonies and at 16% of sites. Its distribution was clumped within the state with the majority of infected colonies and sites occurring in two infection patches. The proportion of polygyne colonies was a strong (positive) predictor of the proportion of infected colonies at a site. Infected monogyne colonies, however, still accounted for nearly 20% of infected colonies, a much higher proportion than anticipated. Several other factors, including the numbers of colonies at a site, precipitation, proximity to commercial waterways and ports, and type of habitat were also retained in the multiple logistic regression model describing T. solenopsae prevalence. The microsporidium appears to adversely affect the occurrence of brood, and possibly the size of S. invicta colonies and the mass of workers. It, however, was not included in the multiple regression model of the number of colonies or the density of ants at a site. Although our findings do not imply causation, they have identified several variables that might influence the epizootiology of T. solenopsae. Future work should concentrate on experimentally manipulating these variables to confirm these relationships.

Effect of mono- and polygyne social forms on transmission and spread of a microsporidium in fire ant populations.

Thelohania solenopsae is a pathogen of the red imported fire ant, Solenopsis invicta, which debilitates queens and eventually causes the demise of colonies. Reductions of infected field populations signify its potential usefulness as a biological control agent. Thelohania solenopsae can be transmitted by introducing infected brood into a colony. The social forms of the fire ant, that is, monogyny (single queen per colony) or polygyny (multiple queens per colony), are associated with different behaviors, such as territoriality, that affect the degree of intercolony brood transfer. T. solenopsae was found exclusively in polygyne colonies in Florida. Non-synchronous infections of queens and transovarial transmission favor the persistence and probability of detecting infections in polygynous colonies. However, queens or alates with the monogyne genotype can be infected, and infections in monogyne field colonies have been reported from Louisiana and Argentina. Limited independent colony-founding capability and shorter dispersal of alate queens with the polygyne genotype relative to monogyne alates may facilitate the maintenance of infections in local polygynous populations. Demise of infected monogyne colonies can be twice as fast as in polygyne colonies and favors the pathogen's persistence in polygyne fire ant populations. The social form of the fire ant reflects different physiological and behavioral aspects of the queen and colony that will impact T. solenopsae spread and ultimate usefulness for biological control.