Canadian researchers have identified a new group of eukaryotes, hemimastigotes, which do not fit into any existing biological kingdom. This discovery, reported by Dalhousie University graduate student Yana Eglit and professor Alastair Simpson in the journal Nature, reveals that hemimastigotes represent a distinct branch of the tree of life, more divergent than animals and fungi. The study highlights the evolutionary significance of the phylum Hemimastigophora, which has been placed outside all established eukaryote supergroups, indicating a novel supra-kingdom-level lineage.
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https://www.cbc.ca/news/technology/hemimastigotes-supra-kingdom-1.4715823Canadian researchers have discovered a new kind of organism that's so different from other living things that it doesn't fit into the plant kingdom, the animal kingdom, or any other kingdom used to classify known organisms.
Two species of the microscopic organisms, called hemimastigotes, were found in dirt collected on a whim during a hike in Nova Scotia by Dalhousie University graduate student Yana Eglit.
A genetic analysis shows they're more different from other organisms than animals and fungi (which are in different kingdoms) are from each other, representing a completely new part of the tree of life, Eglit and her colleagues report this week in the journal Nature.
"They represent a major branch… that we didn't know we were missing," said Dalhousie biology professor Alastair Simpson, Eglit's supervisor and co-author of the new study.
https://www.nature.com/articles/s41586-018-0708-8Almost all eukaryote life forms have now been placed within one of five to eight supra-kingdom-level groups using molecular phylogenetics1,2,3,4. The ‘phylum’ Hemimastigophora is probably the most distinctive morphologically defined lineage that still awaits such a phylogenetic assignment. First observed in the nineteenth century, hemimastigotes are free-living predatory protists with two rows of flagella and a unique cell architecture5,6,7; to our knowledge, no molecular sequence data or cultures are currently available for this group. Here we report phylogenomic analyses based on high-coverage, cultivation-independent transcriptomics that place Hemimastigophora outside of all established eukaryote supergroups. They instead comprise an independent supra-kingdom-level lineage that most likely forms a sister clade to the ‘Diaphoretickes’ half of eukaryote diversity (that is, the ‘stramenopiles, alveolates and Rhizaria’ supergroup (Sar), Archaeplastida and Cryptista, as well as other major groups). The previous ranking of Hemimastigophora as a phylum understates the evolutionary distinctiveness of this group, which has considerable importance for investigations into the deep-level evolutionary history of eukaryotic life—ranging from understanding the origins of fundamental cell systems to placing the root of the tree. We have also established the first culture of a hemimastigote (Hemimastix kukwesjijk sp. nov.), which will facilitate future genomic and cell-biological investigations into eukaryote evolution and the last eukaryotic common ancestor.