Protozoa
Protists are eukaryotic single cell organisms that are not animals, plants and fungi. In fact, these microorganisms are more diverse than the better-known multicellular counterparts[1]. Protists exist in all habitats from deep sea to Antarctic soils to the atmosphere. In an average gram of soil, tens of thousands of protist individuals with sometimes more than thousand species present[2]. Protists perform key roles in the soil[3], such as phototrophic algae and as the major cause of mortality of other microbes such as bacteria, through predation, contributing to the functions of Nutrient cycling and Pest and disease suppression. The diversity and therefore different habitat niches make protists useful indicators such as for plant health, yield and overall soil health[4],[5].
Methods to study protists have long been used and continuously improved but all have some pros and cons. None can cover all protists, as morphology-based ones only can visualize a tiny portion of cultivable or big and fast-swimming protists, while the now predominantly used molecular methods suffer group-specific amplification biases. Overall, method biases need to be known but then they provide important insights into protists and soils in general.
Text by Dr. Stefan Geisen, Laboratory of Nematology, Wageningen University and Research
[1] Geisen S et al. 2020. Soil protist life matters! Soil Organisms 92:189–196
[2] Oliverio AM et al. 2020. The global-scale distributions of soil protists and their contributions to belowground systems. Science Advances 6:eaax8787.
[3] Geisen S et al. 2018. Soil protists: a fertile frontier in soil biology research. FEMS Microbiology Review 42:293-323.
[4] Xiong W et al. 2020. Rhizosphere protists are key determinants of plant health. Microbiome 8:27
[5] Guo S et al. 2021. Protists as main indicators and determinants of plant performance. Microbiome 9:64.