Etymology
The name ''Sappinia'' was named after Mister Sappin-Trouffy, who was a mycologist at the Paris Academy of Sciences, where the genus was first discovered.History of knowledge
The genus ''Sappinia'' was discovered in 1896 by Pierre Augustin Dangeard at the Paris Academy of Sciences. Dangeard noticed white patches on a desiccated culture of horse dung, and when viewed under the microscope, he observed many amoebae. These amoebae were generally binucleated and resembled the myxamoeba life cycle stage present in some plasmodial slime molds; however, Dangeard never observed the plasmodia stage. This was the first species of ''Sappinia'' discovered, ''Sappinia pedata''. The second species discovered, ''Sappinia diploidea'' was originally named ''Amoeba diploidea'', and was first found in 1908 by Max Hartmann and Kurt Nägler. It was isolated from the intestinal material of a lizard; however, it was not thought to be parasitic, as it was not found in 20 other lizards sampled, and a very similar strain was isolated from soil. It was named “diploidea” because the organism was only ever seen in the diploid stage. Nägler stated that there is no true haploid stage; however, further studies have not been able to come to this conclusion, as the nuclei become difficult to discern during sexual reproduction. In 1912 ''A. diploidea'' was transferred to the genus ''Sappinia'' by Alexis Alexeieff. He classified the genus ''Sappinia'' on the basis of being mostly binucleate, with promitotic cell division without the presence of an equatorial plate. Up until very recently these were the only known species of Sappinia, but a new study published in 2015 indicates the discovery of a third species, ''Sappinia platani,'' isolated from the bark of a sycamore tree. Sequencing of its small subunit ribosomal RNA (SSU rRNA) confirmed that it is a member of the genus ''Sappinia'', but genetically distinct from ''S. pedata'' and ''S. diploidea''. Morphologically, ''S. platani'' appears very similar to a typical member of ''Sappinia'', but contains dictyosomes, which had not been reported in this genus previously.Habitat and ecology
Initially, members of ''Sappinia'' were thought to be only coprozoic, as they were first found in animal feces; however, they have now been found in many other habitats, and are considered typical free living amoebae. '' Sappinia'' species are found worldwide in soil, plant litter, and standing decaying plants, freshwater ponds, and have also been found in the feces of horses, lizards, bison, elk, buffalo, and dogs. They are heterotrophic, and feed mostly on bacteria and smaller amoebae.Corsaro, D., Wylezich, C., Walochnik, J., Venditti, D., & Michel, R. 2016: Molecular identification of bacterial endosymbionts of ''Sappinia'' strains. Parasitology Research, 116(2), 549-558. doi:10.1007/s00436-016-5319-4 ''Sappinia'' species, like many other free-living amoebae, play an important role in nutrient cycling in soil. ''Sappinia'' species and their sister genus ''Thecamoeba'' are susceptible to infection by rozellids, that act as endonuclear parasites. ''Sappinia'' species are not generally susceptible to bacterial infection; but, they have been shown to harbor bacterial endosymbionts. In a recent study, Corsaro et al. (2016), found that all of the ''Sappinia'' strains tested harbored distinct species of ''Flavobacterium'' and/or ''Pedobacter,'' which are not known to be commensals of any other free-living amoebae. When these bacterial endosymbionts were isolated, they were unable to grow them in culture, thus they hypothesize that these bacterial species are obligate endosymbionts specific to the genus ''Sappinia''. Although ''Sappinia'' species are generally considered to be non-parasitic, there has been one confirmed case of amoebic encephalitis in a non-immunocompromised 38-year-old male caused by ''S. pedata''.Qvarnstrom, Y., Silva, A. D., Schuster, F., Gelman, B., & Visvesvara, G. 2009: Molecular confirmation of ''Sappinia pedata'' as a causative agent of amoebic encephalitis. The Journal of Infectious Diseases, 199(8), 1139-1142. doi:10.1086/5974Description of the organism
Anatomy and morphology
''Sappinia'' species are naked, lobose amoebe that are generally binucleate. They range in size from 45–76 mm long by 18–38 mm wide. They move using monopodial locomotion, and have a large hyaline region at the anterior end of the cell. The posterior end of the cell is usually jagged; however, there is no distinct uroid (ruffled membrane caused by the movement of cytoplasm out of that region) in motile cells. ''Sappinia'' tend to form distinct clusters in culture, possibly due to congregation where the bacterial count is highest. The sister genus ''Thecamoeba'' does not produce a true theca (shell), but are so named because they contain a very thick, dense glycocalyx, which can be up to 0.5 mm thick. Unlike ''Thecamoeba, Sappina'' species have highly varied glycocalyces depending on the strain and life cycle stage, and none are as thick or well defined as in ''Thecamoeba''. Another difference between ''Thecamoeba'' and ''Sappinia'' is the surface of the dorsal region; ''Thecamoeba'' species tend to have well defined longitudinal ridges on the dorsal surface, whereas ''Sappinia'' species have a smooth dorsal surface, with some small wrinkles along the edges of the cell. ''Sappinia'' species also contain tubular mitochondrial cristae, and have a large contractile vacuole that changes in shape during locomotion. ''S. pedata'' has erect, cyst-like, standing amoebae, while ''S. platani'' has dictyosomes . The erect standing amoebae were originally observed by Dangeard (1896) in ''S. pedata'', and were originally called spores or pedicellate cysts, as they looked similar to the spore-bearing stalks seen in slime molds. Further studies have concluded that there is no cell wall present in these standing amoebae, and they continue to change shape while in the erect position, therefore they are not cysts or spores. ''Sappinia'' species are generally binucleate, with two large, closely apposed nuclei with a flattened, desmosome-like connection. This is a defining feature of ''Sappinia'', as their sister genus ''Thecamoebae'' are mononucleate, and in other binucleate amoebae such as ''Pelomyxa binucleata'', the nuclei are not closely apposed. Each nucleus is between 3.8-4.6 mm in diameter, each with its own central nucleolus that is around 2.3 mm in diameter.Life cycles
''Sappinia'' species have two life cycle stages: a trophozoite, and a cyst. The trophozoite is the heterotrophic feeding stage described previously, and the cyst is formed from the fusion of two trophozoites. The cysts are usually round, and between 30–34 mm in diameter. In 1908, Nägler was working on ''S. diploidea'' and after 2–3 weeks in culture he observed 2 equal size trophozoites encyst together in a double wall. Nägler stated that first the pairs of nuclei in each trophozoite fuse, and then the cells fuse together in the cyst. The amoeba that arises from the cyst is thought to have two haploid nuclei, making it a diploid, thus there is no true haploid life cycle stage. Many other studies have found these bicellular, double walled cysts in both ''S. diploidea'' and ''S. pedata''; however, the fusion of nuclei has never been documented, as they become very difficult to detect during this process, therefore the exact process of sexual reproduction (including the presence of a haploid stage) are not currently known. The encystation process is likely to be used for sexual reproduction''.'' Nägler had also stated that when exposed to dry conditions for long periods of time, the trophozoites did not encyst, further supporting the hypothesis that the cysts are used for sexual reproduction, and not as protection from desiccation. ''Sappinia'' species also undergo asexual reproduction, as described by Nägler in 1908. First the two nuclei divide, and two pairs of nuclei are formed in parallel configuration. Then the nuclei cross and become anti-parallel, so that each daughter cell receives half of each of the two nuclei. Cell division then occurs, and binucleate trophozoites are formed. Although the majority of cells are binucleate, many studies have observed cells with one or four nuclei, and some studies have also observed cells with three, six, and eight nuclei. According to Walochnik et al. (2010), Nägler observed that the rare, mononucleate cells “mostly derived from copulation when one of the copulating amoebae degraded so that the final amoeba was a product of parthenogenesis, the nuclei of one and the same individual fusing, or, but very rarely, derived from cells in which the reduced gametic nuclei of the copulating amoebae fused”.