title: Morphological Study of the Encystment and Excystment of Vermamoeba vermiformis Revealed Original Traits.
abstract: Free-living amoebae are ubiquitous protozoa commonly found in water. Among them, Acanthamoeba and Vermamoeba (formerly Hartmannella) are the most represented genera. In case of stress, such as nutrient deprivation or osmotic stress, these amoebae initiate a differentiation process, named encystment. It leads to the cyst form, which is a resistant form enabling amoebae to survive in harsh conditions and resist disinfection treatments. Encystment has been thoroughly described in Acanthamoeba but poorly in Vermamoeba. Our study was aimed to follow the encystment/excystment processes by microscopic observations. We show that encystment is quite rapid, as mature cysts were obtained in 9 h, and that cyst wall is composed of two layers. A video shows that a locomotive form is likely involved in clustering cysts together during encystment. As for Acanthamoeba, autophagy is likely active during this process. Specific vesicles, possibly involved in ribophagy, were observed within the cytoplasm. Remarkably, mitochondria rearranged around the nucleus within the cyst, suggesting high needs in energy. Unlike Acanthamoeba and Naegleria, no ostioles were observed in the cyst wall suggesting that excystment is original. During excystment, large vesicles, likely filled with hydrolases, were found in close proximity to cyst wall and digest it. Trophozoite moves inside its cyst wall before exiting during excystment. In conclusion, Vermamoeba encystment/excystment displays original trends as compare to Acanthamoeba.
authors.affiliation: Université de Poitiers, UMR CNRS 7267, Ecologie et Biologie des Interactions (EBI), 1 rue G. Bonnet, 86073, Poitiers Cedex, France; Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 194223, Saint-Petersburg, Russia.
authors.forename: Emilie
authors.initials: E
authors.lastname: Fouque
authors.forename: Marina
authors.initials: M
authors.lastname: Yefimova
authors.forename: Marie-Cécile
authors.initials: MC
authors.lastname: Trouilhé
authors.forename: Nathalie
authors.initials: N
authors.lastname: Quellard
authors.forename: Béatrice
authors.initials: B
authors.lastname: Fernandez
authors.forename: Marie-Hélène
authors.initials: MH
authors.lastname: Rodier
authors.forename: Vincent
authors.initials: V
authors.lastname: Thomas
authors.forename: Philippe
authors.initials: P
authors.lastname: Humeau
authors.forename: Yann
authors.initials: Y
authors.lastname: Héchard
mesh_terms: D016840:Lobosea / Q000166:cytology* / Q000502:physiology*; D018715:Microscopy, Video; D033761:Spores, Protozoan / Q000166:cytology* / Q000502:physiology*; D013997:Time Factors
keywords: Autophagy; Hartmannella; electron microscopy; free-living amoeba