Taxonomy And Diversity Of Soil Hypotrichous Ciliates

Ciliates constitute a major link between the highly productive and nutrient retaining micro-bial loop and the metazoans of the classical food web.They are abundant in terrestrial as well as in aquatic systems.Ciliates not only play an important role in matter cycling of natural ecosystems,but also an important indicator in the environmental evaluation.The subclass Hypotrichia is one of the most morphologically diverse groups of ciliates,and recent faunistic studies have revealed a high diversity of hypotrichous ciliates in soil ecosystem.In this paper,the morphology,ontogeny and molecular phylogeny of ten soil hypotrichs were studied based on modern techniques: microscopic observation in vivo,silver-staining technique,and molecular methods.The main achievements are following:1.MorphologyDescribed and established 2 new genera(Metaoxytricha and Simplicistomum),4 novel species(Pseudourostyla guizhouensis sp.n.,Sterkiella multicirrata sp.n.,Metaoxytricha mollis sp.n.,and Simplicistomum xianense sp.n.).Morphology data of Hemicycliostyla franzi,Bakuella granulifera,Sterkiella cavicola,Monomicrocaryon euglenivorum fimbricirratum,Gonostomum affine,and Urosomoida agiliformis were also supplemented.The 2 new genera are defined as following:(1)Metaoxytricha gen.n.Body flexible,adoral zone of membranelles formed like a question mark.Endoral and paroral in Oxytricha-pattern.Three frontal cirri,one buccal cirrus,four frontoventral cirri,three postoral ventral cirri,two pretransverse ventral cirri,and four transverse cirri present.One right and one left marginal row,dorsomarginal kinety present,caudal cirri associated with dorsal kineties 1,2 and 4.(2)Simplicistomum gen.n.Flexible oxytrichids,undulating membranes absent or with a vestigial undulating membrane,one left and one right marginal row,dorsomarginal kinety present,three caudal cirri associated with dorsal kineties 1,2 and 4.Morphological characters of 4 new species are following:(1)Pseudourostyla guizhouensis sp.n.Body elongate-elliptical,really flexible,measuring about 240 × 70 ?m in vivo.Adoral zone consisting of 63 membranelles on average.Cortical granules colorless and spherical.One contractile vacuole positioned to left margin,usually with two collecting canals.12–16 frontal cirri;one buccal cirri;two frontoterminal cirri;about 17 midventral pairs;five to seven transverse cirri.Three or four left,and invariably two right marginal rows.Six or seven longitudinal dorsal kineties,caudal cirri absent.26–40 macronuclear nodules and two to five micronuclei.(2)Sterkiella multicirrata sp.n.Cell elliptical and rigid,size 110–180 × 45–75 ?m in vivo.On average 35 adoral membranelles.Cortical granules absent.One contractile vacuole near left body margin.Totally 19 or 20 frontal-ventral-transverse cirri,consisting of three frontal,one buccal,five frontoventral,four or five ventral,two pretransverse,and four(sometimes five)transverse cirri.One left and one right marginal row.Six dorsal kineties in Oxytricha-pattern,three caudal cirri.Four to five macronuclear nodules,about four micronuclei.(3)Metaoxytricha mollis sp.n.Body elongate and posterior end narrowly rounded,size 95–145 × 30–60 ?m in vivo.Cortical granules citrine-yellow.Contractile vacuole near left margin.Two macronuclear nodules and one to three micronuclei.26–34 adoral membranelles.Endoral and paroral in Australocirrus-pattern.Three frontal,one buccal,four frontoventral,three postoral ventral,two pretransverse and four transverse cirri,consistently.One right and one left marginal row.Dorsal kineties in Oxytricha-pattern,three caudal cirri.Metaoxytricha gen.n.was established based on the ventral character.(4)Simplicistomum xianense sp.n.Cell elongate and flattened,size 85–130 × 30–50 ?m.Cortical granules absent.One contractile vacuole near left margin.Two ellipsoidal macronuclear nodules,and two micronuclei.Adoral zone consists of 24–32 adoral membranelles.Invariably three frontal cirri,one buccal cirri,four frontoventral cirri,three postoral ventral cirri,five transverse cirri and two pretransverse cirri.One right and one left marginal row each side.Six dorsal kineties and three caudal cirri.Simplicistomum gen.n was established based on the character of undulating membrane.2.Morphogenesis(1)Morphogenesis of Sterkiella multicirrata sp.n.is in Oxytricha pattern,the formation of new frontal-ventral-transverse cirri in a 1: 2: 3: 3: 5(or 6): 5(or 6)pattern.Totally,the ontogenetic process of the novel species shows the morphogenesis in the genus Sterkiella is conservative.(2)Two reorganizers of Pseudourostyla guizhouensis sp.n.were found during its physiological regeneration: the proximal portion of the parental adoral zone is resorbed and replaced by new membranelles;the new left and right marginal cirral rows develop from a unit of anlage on each side;the dorsal kinety anlagen originate in parental rows.These main process of reorganization reveals the morphogenesis in the genus Pseudourostyla is conservative.(3)For Monomicrocaryon euglenivorum fimbricirratum,kinety 4 originates by a split of kinety 3,which corresponds with the main character of genus Monomicrocaryon.(4)Morphogenetic characters of Gonostomum affine and Urosomoida agiliformis were provided and compared with recent researches.3.Molecular phylogenySSU rRNA gene sequences of the 4 new species were analysed,and the phylogenetic position of them were discussed:(1)The genus Pseudourostyla is monophyletic clade,and P.guizhouensis sp.n.is sister to P.cristata.Genera Hemicycliostyla,Pseudourostyla,and Trichototaxis form a polyphyletic group.(2)The 7 Sterkiella species we chose fell into 5 clade,and Sterkiella multicirrata sp.n.clusters well with S.tetracirrata,which is correspond with the morphogenetic data.(3)Metaoxytricha mollis sp.n.clusters with dorsomarginalia,indicates that the dorsal characters likely accounting for a larger proportion in the classification of hypotrichs.(4)Simplicistomum xianense sp.n.consistently fell into clade Stylonychinae,however,the flexible cortex is the main character of Oxytrichinae,hence,the subfamily standard classification of S.xianense sp.n.remains uncertain.