Neither animal, plant, fungus nor familiar protozoan, a strange microbe that sits in its own “supra-kingdom” of life foretells incredible biodiversity yet to be discovered by new sequencing technologies.
Quanta Magazine said:The tree of life just got another major branch. Researchers recently found a certain rare and mysterious microbe called a hemimastigote in a clump of Nova Scotian soil. Their subsequent analysis of its DNA revealed that it was neither animal, plant, fungus nor any recognized type of protozoan — that it in fact fell far outside any of the known large categories for classifying complex forms of life (eukaryotes). Instead, this flagella-waving oddball stands as the first member of its own “supra-kingdom” group, which probably peeled away from the other big branches of life at least a billion years ago.
“It’s the sort of result you hope to see once in a career,” said Alastair Simpson, a microbiologist at Dalhousie University who led the study.
Impressive as this finding about hemimastigotes is on its own, what matters more is that it’s just the latest (and most profound) of a quietly and steadily growing number of major taxonomic additions. Researchers keep uncovering not just new species or classes but entirely new kingdoms of life — raising questions about how they have stayed hidden for so long and how close we are to finding them all.
Yana Eglit is a Dalhousie graduate student dedicated to discovering novel lineages of the single-cell eukaryotes called protists. While hiking in Nova Scotia on a cold spring day in 2016, she fell back from her friends to scrape a few grams of dirt into a plastic tube. (Such impromptu soil sampling, she said, is “a professional hazard.”) Back in the lab, Eglit soaked her sample in water, and over the next month she periodically peeked at it through a microscope for signs of unusual life.
Late one evening, something odd in the sample caught her eye. An elongated cell radiating whiplike flagella was “awkwardly swimming, as though it didn’t realize it had all these flagella that could help it move,” Eglit said. Under a more powerful scope, she saw it fit the description of a hemimastigote, a rare kind of protist that was notoriously hard to cultivate. The next morning, the lab was abuzz with excitement over the opportunity to describe and sequence the specimen. “We dropped everything,” she recalled.
Hemimastigotes represent one of a handful of Rumsfeldian “known unknown” protist lineages — moderately well-described groups whose positions on the tree of life are not precisely known because they are difficult to culture in a lab and sequence. Protistologists have used peculiarities of hemimastigotes’ structure to infer their close relatives, but their guesses were “‘shotgunned’ all over the phylogeny,” Simpson said. Without molecular data, lineages like hemimastigotes remain orphans of unknown ancestry.
But a new method called single-cell transcriptomics has revolutionized such studies. It enables researchers to sequence large numbers of genes from just one cell. Gordon Lax, another graduate student in the Simpson lab and an expert on this method, explained that for hard-to-study organisms like hemimastigotes, single-cell transcriptomics can produce genetic data of a quality previously reserved for more abundant cells, making deeper genomic comparisons finally possible.
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