''Hatena arenicola'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of single-celled

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

s discovered in 2000, and first reported in 2005. It was discovered by Japanese biologists Noriko Okamoto and Isao Inouye at the University of Tsukuba, and they gave the scientific description and formal name in 2006. The species is a

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their ...

, and can resemble a

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

at one stage of its life, in which it carries a

photosynthesizing Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

inside itself, or an

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

, acting as

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

in another stage of its life. Researchers believe that this organism is in the process of

secondary endosymbiosis Symbiogenesis (endosymbiotic theory, or serial endosymbiotic theory,) is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possi ...

, in which one organism is incorporated into another, resulting in a completely new life form.

Discovery

''H. arenicola'' was first noticed as

algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompas ...

in 2000 from Isonoura beach in Japan. It was found in the area of moderately sheltered sandy shore, where a number of algae surfaced during tsunami. The specimens were present in the upper edge of the seepage face. It can be found throughout the year, except in winter. It was originally believed to be a new green alga. However, it was discovered that the chlorophyll-bearing

plastids The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosymbiotic cyanobac ...

were independent of the

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

, indicating that they were separate but temporary

endosymbiotic An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...

organisms.

Description

''H. arenicola'' is a protist with one rounded cell having two

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

for locomotion. It feeds on algae using a complex feeding tube when it leads an independent life. The feeding tube, however, is replaced by an endosymbiotic alga. The algal endosymbiont is a

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

from the genus ''

Nephroselmis ''Nephroselmis'' is a genus of green algae. It has been placed in the family Nephroselmidaceae, although a 2009 study suggests that it should be separated into its own class, Nephroselmidophyceae. One species can be an endosymbiont of ''Hatena ...

''. The endosymbiont not only acts as feeding apparatus, but also as an eye spot, by which it probably helps the protist for directional movements towards light (

phototaxis Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive li ...

). ''H. arenicola'' cannot divide without containing the endosymbiont. But, unlike a fully integrated organelle, the ''Nephroselmis'' alga does not divide along with the host cell. When the host cell divides, one of the daughter cells receives the ''Nephroselmis'' cell and the other daughter returns to a

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

lifestyle. Hence, the mother protist gives rise to green-coloured and white-coloured daughter cells. The latter behaves like a predator until it ingests a ''Nephroselmis'' green alga. The alga then loses its flagella and

cytoskeleton The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...

, while the ''Hatena'', now a host, switches to photosynthetic nutrition, gains the ability to move towards light and loses its feeding apparatus. Thus, the protist exhibits an unusual life cycle of alternating

autotrophy An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

and heterotrophy. Genetic sequencing (of 18S

rRNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosoma ...

gene) revealed that the protist can harbour at least three distinct strains of ''Nephroselmis rotunda''. The

generic Generic or generics may refer to: In business * Generic term, a common name used for a range or class of similar things not protected by trademark * Generic brand, a brand for a product that does not have an associated brand or trademark, other ...

name is from a Japanese interjection roughly meaning "enigmatic" or "unusual".

The symbiont

The symbiotic ''

'' is different from the free-living form. It retains its

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...

and

plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosy ...

, while other organelles including

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

Golgi body The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles insi ...

, and

endomembrane The endomembrane system is composed of the different membranes (endomembranes) that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes ...

system are degraded. The

is also comparatively enlarged up to ten times the normal size of free-living form. The enlarged plastid is compensated by reduced cytoplasmic components.

References

External links

Pictures of ''Hatena''Taxonomy at UniProtClassification at Encyclopedia of Life
{{Taxonbar, from=Q143705 Endosymbiotic events Species described in 2006 Katablepharida

Discovery

Description

The symbiont

See also

References

External links