Parakaryon myojinensis

Drawing of Parakaryon myojinensis showing its unique cell structure with cell wall, single nuclear membrane, and a single large spiral endosymbiont (seen in section), a combination found neither in prokaryotes nor eukaryotes. Cell is 10 μm long.
Approximate location of Myōjin Knoll, where the specimen was found.

Parakaryon myojinensis is a single-celled organism known from a single specimen, described in 2012. It has features of both prokaryotes and eukaryotes but is apparently distinct from either group, making it unique among organisms so far discovered.[1]

Classification

It is not clear whether P. myojinensis can be classified as either a eukaryote or a prokaryote, the two kinds of organisms known so far. The newly discovered organism has a nucleus and other endosymbionts (organisms living within other cells), so would appear to be a eukaryote. However the nuclear membrane is a single layer, not a double layer as in other eukaryotes, and the DNA is stored in filaments. There is no endoplasmic reticulum, Golgi apparatus, cytoskeleton, mitochondria or nuclear pores. Ribosomes are found both inside and outside the nucleus. Adding to the difficulties of classification, only one instance of this organism has been discovered to date, and so scientists have not been able to observe it further.[2][3][4]

Name

The generic name, Parakaryon comes from Greek παρά (pará, next to) and κάρυον (káryon, kernel, nucleus) and reflects its position between eu- and prokaryotes. The specific name, myojinensis reflects the locality where the samples have been collected: the hydrothermal vents at the Myōjin Knoll (明神海丘,[5] 32°06.2′N, 139°52.1′E) off the coast of Japan at a depth of 1240 m.[1]

References

  1. 1 2 Yamaguchi M, Mori Y, Kozuka Y, Okada H, Uematsu K, Tame A, Furukawa H, Maruyama T, Worman CO, Yokoyama K (2012). "Prokaryote or eukaryote? A unique microorganism from the deep sea". J Electron Microsc (Tokyo). 61 (6): 423–431. doi:10.1093/jmicro/dfs062.
  2. ↑ Nick Lane (2015). "Epilogue: From the Deep". The Vital Question: Energy, Evolution, and the Origins of Complex Life. W.W.Norton and Company. pp. 281–290. ISBN 978-0-393-08881-6.
  3. ↑ Prokaryote or eukaryote? A unique microorganism from the deep sea
  4. ↑ Evolution of complex life on Earth, take 2
  5. ↑ Fumitoshi MURAKAMI, The Forming Mechanism of the Submarine Caldera on Myojin Knoll in the Northern Part of the Izu-Ogasawara (Bonin) Arc
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