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Protists are the most diverse eukaryotes. These microbes are keystone organisms of soil ecosystems and regulate essential processes of soil fertility such as nutrient cycling and plant growth. Despite this, protists have received little scientific attention, especially compared to bacteria, fungi and nematodes in soil studies. Recent methodological advances, particularly in molecular biology techniques, have made the study of soil protists more accessible, and have created a resurgence of interest in soil protistology. This ongoing revolution now enables comprehensive investigations of the structure and functioning of soil protist communities, paving the way to a new era in soil biology. Instead of providing an exhaustive review, we provide a synthesis of research gaps that should be prioritized in future studies of soil protistology to guide this rapidly developing research area. Based on a synthesis of expert opinion we propose 30 key questions covering a broad range of topics including evolution, phylogenetics, functional ecology, macroecology, paleoecology, and methodologies. These questions highlight a diversity of topics that will establish soil protistology as a hub discipline connecting different fundamental and applied fields such as ecology, biogeography, evolution, plant-microbe interactions, agronomy, and conservation biology. We are convinced that soil protistology has the potential to be one of the most exciting frontiers in biology.

The monophyly of the litostomes was tested using nine newly sequenced and four previously unpublished small subunit ribosomal RNA (SSrRNA) gene sequences from free-living Haptoria as well as from endosymbiotic Trichostomatia: the vestibuliferids Balantidium coli and Isotricha prostoma, the cyclotrichiid Mesodinium pulex, and the haptorids Loxophyllum rostratum, Dileptus sp., Enchelyodon sp., Enchelys polynucleata, Epispathidium papilliferum (isolates A and B), Spathidium stammeri, Arcuospathidium muscorum, Arcuospathidium cultriforme, and the unusual Teuthophrys trisulca. Phylogenetic analyses depicted the litostomes as a monophyletic group consisting of the trichostomes (subclass Trichostomatia) and the free-living haptorians (subclass Haptoria). The cyclotrichiids Mesodinium and Myrionecta (order Cyclotrichiida) branched either basally within or outside the Litostomatea. In most analyses, the haptorians did not receive support as a monophyletic group. Instead, Dileptus branched basally to all litostome taxa, and Epispathidium papilliferum grouped with the Subclass Trichostomatia. Some subgroupings, however, of haptorian genera corresponded to suggested superfamilial taxa (e.g., orders Spathidiida and Pleurostomatida). Within the monophyletic trichostomes, we can distinguish three clades: (1) an Australian clade; (2) the order Entodiniomorphida; and (3) the order Vestibuliferida. However, Balantidium, currently classified in the Vestibuliferida, did not group with the other vestibuliferids, suggesting that this order may be paraphyletic.

Item does not contain fulltext, We performed a comparative morphological and molecular study on oxytrichid and urostylid stichotrichs (= part of the former hypotrichs). Included are new small subunit (18S) ribosomal RNA (rRNA) gene sequences from five rare oxytrichids (Gonostomum namibiense, Cyrtohymena citrina, Hemiurosoma terricola, Onychodromopsis flexilis, Orthoamphisiella breviseries) and published sequences, based on cultures provided by the senior author, of two key stichotrichid genera, viz., Gastrostyla and Engelmanniella. These and other sequences, altogether 27 species representing 23 genera, were used to analyze how 18S rRNA-based phylogenetic trees can be reconciled with the morphological and ontogenetical data. In 18S rRNA trees, the oligotrichine family Halteriidae invariably clusters within the oxytrichid clade, usually near Oxytricha granulifera, type species of the genus. This position is hardly supported by morphological and ecological evidence and, especially, it contradicts the current ontogenetic findings; possibly, it is an artifact caused by taxa undersampling and/or special molecular evolutionary events. In contrast, most morphological and DNA sequence data of the stichotrichs can be harmonized with the CEUU (Convergent Evolution of Urostylids and Uroleptids) hypothesis which suggests that the urostylid midventral pattern evolved from an oxytrichine ancestor, developing a second time within the Oxytrichidae. The systematic position of one of the two key genera could be clarified with the 18S rRNA sequences: Gastrostyla is a stylonychine oxytrichid. Based on the molecular data and a reassessment of ontogenesis, a new genus, Styxophrya nov. gen., is established for Onychodromus quadricornutus Foissner, Schlegel & Prescott, 1987. (C) 2004 Elsevier GmbH. All rights reserved.