Environmental DNA reveals protist lineages without described representatives
An environmental genetic survey found many protist lineages with no formally described member in its broad sequence groups. The group encompasses diverse nucleated organisms beyond the animal, fungal and plant kingdoms. The peer-reviewed work also identified 13 candidate deep lineages. Its percentages concern groups of related sequences, not a count of Earth’s species, and geographic gaps still shape the available data.
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Broad clusters lack described organisms
Genetic traces from environmental samples exposed major gaps in the description of protists, nucleated organisms distinct from animals, fungi and plants. In one peer-reviewed survey, researchers screened 32,520 assembled metagenomes. After removing non-protist groups and singletons, they examined 9,543 broad clusters based on an 85 per cent sequence-similarity threshold. In 81 per cent, no described representative was available. These clusters capture deeper relationships rather than providing a species census.[1]
Long gene sequences reveal candidate branches
The search recovered 157,956 long sequences of a ribosomal RNA gene from 18,445 datasets. Ribosomal RNA is part of the cell’s protein-making machinery and helps compare evolutionary relationships. Whole-metagenome searches can recover sequences missed by targeted amplification methods. The analysis identified 13 candidate deeply divergent lineages. Partial genomes obtained from individual cells strengthened some proposed relationships, while conflicting signals from different genes left other placements uncertain. Their cells and lifestyles still need characterization.[1]
Sampling shapes the environmental comparisons
Freshwater environments carried high diversity within the dataset, and wetlands and sediments yielded traces of poorly known lineages. Coverage was geographically uneven, with substantial representation from North America and Central Europe. Assembly errors and failure to recover rare organisms remain possible. Diversity curves had not levelled off, indicating that additional sampling could recover more groups in these environments. Finding sequences together can suggest ecological associations, but cannot establish predation or symbiosis.[1]
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