Researchers identify archaeon with smallest known archaeal genome, 189 proteins, depending on a host
Scientists have identified Candidatus Sukunaarchaeum mirabile, an archaeon with a 238,034 base-pair genome encoding 189 proteins, according to Laboratory News and TechTimes, which both report the study published in Current Biology. The organism has retained genes for copying DNA and making proteins but has lost almost all genes for producing nutrients and energy, so it likely depends on another organism, though no host has yet been identified. The genome was less than half the size of the previous archaeal record, Nanoarchaeum equitans, at 490,000 base pairs.
Bottom line — Researchers at the University of Nottingham and Tsukuba plan to find the organism's host and observe the cell directly, which has never been imaged.
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TechTimes reports the genome was assembled from a single marine dinoflagellate cell collected near Shimoda, Japan, and that the team sequenced it twice using two independent methods before trusting the result.
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Quanta Magazine, quoted by TechTimes, reports Takuro Nakayama saying the cell challenges how metabolism is used to define life, while Thijs Ettema of Wageningen University questioned at what point organisms should be called alive.
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According to TechTimes, Sukunaarchaeum's 189 proteins are fewer than many large viruses, but unlike viruses it encodes its own ribosomes, which is the criterion used in the 2008 Raoult and Forterre framework.
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Wikipedia notes the genus name refers to Sukunabikona, a Shinto deity linked to hot springs, and that Ryo Harada of Dalhousie University led the initial preprint.
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TechTimes reports phylogenetic placement remains ambiguous, with maximum-likelihood and Bayesian analyses disagreeing on its position in the archaeal tree.
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Laboratory News and TechTimes quote Thorsten Allers of the University of Nottingham saying the organism may be close to the minimum genetic information needed for an independent cell.
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TechTimes reports that for comparison, the JCVI-syn3.0 synthetic bacterium had 531,560 base pairs and 473 genes, and was free-living.
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Mart Krupovic of Institut Pasteur, quoted by Nautilus Magazine via TechTimes, called the finding remarkable and said how little is still known about the surrounding world.