Genus of about nine species of freshwater amoeboids.

- Paulinella

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Membrane-bound organelle found in the cells of plants, algae, and some other eukaryotic organisms.

Plant cells with visible chloroplasts.
Plastid types
Leucoplasts in plant cells.
There is an illustration of stages depicted by the diagram mentioned above in which it is shown inter-conversion of Plastids

A later primary endosymbiosis event occurred in photosynthetic Paulinella amoeboids about 90–140 million years ago.


Type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells.

Chloroplasts visible in the cells of Bryum capillare, a type of moss
Euglena, a euglenophyte, contains secondary chloroplasts from green algae.
Chlorarachnion reptans is a chlorarachniophyte. Chlorarachniophytes replaced their original red algal endosymbiont with a green alga.
Scanning electron micrograph of Gephyrocapsa oceanica, a haptophyte.
The photosynthetic pigments present in their chloroplasts give diatoms a greenish-brown color.
Ceratium furca, a peridinin-containing dinophyte
Karenia brevis is a fucoxanthin-containing dynophyte responsible for algal blooms called "red tides".
Dinophysis acuminata has chloroplasts taken from a cryptophyte.
Chloroplast DNA replication via multiple D-loop mechanisms. Adapted from Krishnan NM, Rao BJ's paper "A comparative approach to elucidate chloroplast genome replication."
Over time, base changes in the DNA sequence can arise from deamination mutations. When adenine is deaminated, it becomes hypoxanthine, which can pair with cytosine. During replication, the cytosine will pair with guanine, causing an A --> G base change.
Transmission electron microscope image of a chloroplast. Grana of thylakoids and their connecting lamellae are clearly visible.
Instead of an intermembrane space, glaucophyte algae have a peptidoglycan wall between their inner and outer chloroplast membranes.
Granum-stroma assembly structure The prevailing model of the granum-stroma assembly is stacks of granal thylakoids wrapped by right-handed helical stromal thylakoids which are connected to large parallel sheets of stromal thylakoids and adjacent right-handed helices by left-handed helical structures. (Based on ).

With one exception (the amoeboid Paulinella chromatophora), all chloroplasts can probably be traced back to a single endosymbiotic event, when a cyanobacterium was engulfed by the eukaryote.


Leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms.

Internal symbiont: mitochondrion has a matrix and membranes, like a free-living alphaproteobacterial cell, from which it may derive.
Konstantin Mereschkowski's 1905 tree-of-life diagram, showing the origin of complex life-forms by two episodes of symbiogenesis, the incorporation of symbiotic bacteria to form successively nuclei and chloroplasts.
One model for the origin of mitochondria and plastids
Modern endosymbiotic theory posits that simple life forms merged, forming cell organelles, like mitochondria.
Kwang Jeon's experiment: [I] Amoebae infected by x-bacteria [II] Many amoebae become sick and die [III] Survivors have x-bacteria living in their cytoplasm [IV] Antibiotics kill x-bacteria: host amoebae die as now dependent on x-bacteria.
Mitochondria of a mammal lung cell visualized using Transmission Electron Microscopy
Diagram of endomembrane system in eukaryotic cell
The human mitochondrial genome has retained genes encoding 2 rRNAs, 22 tRNAs, and 13 redox proteins.
Simplified chart showing the three main mergers of the endosymbiotic theory

Using the example of the freshwater amoeboid, however, Paulinella chromatophora, which contains chromatophores found to be evolved from cyanobacteria, Keeling and Archibald argue that this is not the only possible criterion; another is that the host cell has assumed control of the regulation of the former endosymbiont's division, thereby synchronizing it with the cell's own division.


The Archaeplastida (or kingdom Plantae sensu lato "in a broad sense"; pronounced /ɑːrkɪ'plastɪdə/) are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes.

The glaucophyte Glaucocystis
The rhodophyte Laurencia
The chlorophyte Stigeoclonium

All other groups which have chloroplasts, besides the amoeboid genus Paulinella, have chloroplasts surrounded by three or four membranes, suggesting they were acquired secondarily from red or green algae.


Any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.

A representation of the endosymbiotic theory
An overview of the endosymbiosis theory of eukaryote origin (symbiogenesis).
Diagram of cospeciation, where parasites or endosymbionts speciate or branch alongside their hosts. This process is more common in hosts with primary endosymbionts.
Pea aphids are commonly infested by parasitic wasps. Their secondary endosymbionts attack the infesting parasitoid wasp larvae promoting the survival of both the aphid host and its endosymbionts.

Paulinella chromatophora is a freshwater amoeboid which has recently (evolutionarily speaking) taken on a cyanobacterium as an endosymbiont.


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.

Schematic of photosynthesis in plants. The carbohydrates produced are stored in or used by the plant.
Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation. Dark red and blue-green indicate regions of high photosynthetic activity in the ocean and on land, respectively.
Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.
Light-dependent reactions of photosynthesis at the thylakoid membrane
The "Z scheme"
Overview of the Calvin cycle and carbon fixation
Overview of C4 carbon fixation
Plant cells with visible chloroplasts (from a moss, Plagiomnium affine)
Portrait of Jan Baptist van Helmont by Mary Beale, c.1674
Melvin Calvin works in his photosynthesis laboratory.
The leaf is the primary site of photosynthesis in plants.
Absorbance spectra of free chlorophyll a ( blue ) and b ( red ) in a solvent. The action spectra of chlorophyll molecules are slightly modified in vivo depending on specific pigment–protein interactions.

The chlorarachniophytes and 3 species of Paulinella in the phylum Cercozoa—clade Rhizaria (unicellular)


Cyanobacteria, also known as Cyanophyta, are a phylum of Gram-negative bacteria that obtain energy via photosynthesis.

Cyanobacteria are found almost everywhere. Sea spray containing marine microorganisms, including cyanobacteria, can be swept high into the atmosphere where they become aeroplankton, and can travel the globe before falling back to earth.
• Unicellular: (a) Synechocystis and (b) Synechococcus elongatus
• Non-heterocytous: (c) Arthrospira maxima,• False- or non-branching heterocytous: (f) Nostoc• True-branching heterocytous: (h) Stigonema
Outer and plasma membranes are in blue, thylakoid membranes in gold, glycogen granules in cyan, carboxysomes (C) in green, and a large dense polyphosphate granule (G) in pink
Environmental impact of cyanobacteria and other photosynthetic microorganisms in aquatic systems. Different classes of photosynthetic microorganisms are found in aquatic and marine environments where they form the base of healthy food webs and participate in symbioses with other organisms. However, shifting environmental conditions can result in community dysbiosis, where the growth of opportunistic species can lead to harmful blooms and toxin production with negative consequences to human health, livestock and fish stocks. Positive interactions are indicated by arrows; negative interactions are indicated by closed circles on the ecological model.
Diagnostic Drawing: Cyanobacteria associated with tufa: Microcoleus vaginatus
(1) Cyanobacteria enter the leaf tissue through the stomata and colonize the intercellular space, forming a cyanobacterial loop.
(2) On the root surface, cyanobacteria exhibit two types of colonization pattern; in the root hair, filaments of Anabaena and Nostoc species form loose colonies, and in the restricted zone on the root surface, specific Nostoc species form cyanobacterial colonies.
(3) Co-inoculation with 2,4-D and Nostoc spp. increases para-nodule formation and nitrogen fixation. A large number of Nostoc spp. isolates colonize the root endosphere and form para-nodules.
Live cyanobionts (cyanobacterial symbionts) belonging to Ornithocercus dinoflagellate host consortium
(a) O. magnificus with numerous cyanobionts present in the upper and lower girdle lists (black arrowheads) of the cingulum termed the symbiotic chamber.
(b) O. steinii with numerous cyanobionts inhabiting the symbiotic chamber.
(c) Enlargement of the area in (b) showing two cyanobionts that are being divided by binary transverse fission (white arrows).
Light microscope view of cyanobacteria from a microbial mat
Types of cell death according to the Nomenclature Committee on Cell Death (upper panel; and proposed for cyanobacteria (lower panel). Cells exposed to extreme injury die in an uncontrollable manner, reflecting the loss of structural integrity. This type of cell death is called "accidental cell death" (ACD). “Regulated cell death (RCD)” is encoded by a genetic pathway that can be modulated by genetic or pharmacologic interventions. Programmed cell death (PCD) is a type of RCD that occurs as a developmental program, and has not been addressed in cyanobacteria yet. RN, regulated necrosis.
Synechococcus uses a gliding technique to move at 25 μm/s. Scale bar is about 10 µm.
Based on data: nodes (1–10) and stars representing common ancestors from Sánchez-Baracaldo et al., 2015, timing of the Great Oxidation Event (GOE), the Lomagundi-Jatuli Excursion, and Gunflint formation. Green lines represent freshwater lineages and blue lines represent marine lineages are based on Bayesian inference of character evolution (stochastic character mapping analyses).
Tree of Life in Generelle Morphologie der Organismen (1866). Note the location of the genus
Nostoc with algae and not with bacteria (kingdom "Monera")
Cyanobacteria cultured in specific media: Cyanobacteria can be helpful in agriculture as they have the ability to fix atmospheric nitrogen in soil.
Spirulina tablets
Stromatolites left behind by cyanobacteria are the oldest known fossils of life on Earth. This fossil is one billion years old.
Oncolitic limestone formed from successive layers of calcium carbonate precipitated by cyanobacteria
Oncolites from the Late Devonian Alamo bolide impact in Nevada
{{center|Cyanobacterial remains of an annulated tubular microfossil Oscillatoriopsis longa{{hsp}}<ref>{{cite journal |doi=10.1111/pala.12374 |title=First record of Cyanobacteria in Cambrian Orsten deposits of Sweden |year=2018 |last1=Castellani |first1=Christopher |last2=Maas |first2=Andreas |last3=Eriksson |first3=Mats E. |last4=Haug |first4=Joachim T. |last5=Haug |first5=Carolin |last6=Waloszek |first6=Dieter |journal=Palaeontology |volume=61 |issue=6 |pages=855–880 |s2cid=134049042}}</ref>
Cyanobacteria activity turns Coatepeque Caldera lake a turquoise color
Cyanobacterial bloom near Fiji
Cyanobacteria in Lake Köyliö.

The description of another independent and more recent primary endosymbiosis event between a cyanobacterium and a separate eukaryote lineage (the rhizarian Paulinella chromatophora) also gives credibility to the endosymbiotic origin of the plastids.

List of sequenced plastomes

Genome of a plastid, a type of organelle found in plants and in a variety of protoctists.

The 156 kb plastome gene map of Nicotiana tabacum.
The 154 kb plastid genome map of a model flowering plant (Arabidopsis thaliana: Brassicaceae).
The highly reduced, 27 kb plastome map of the parasitic Hydnora visseri.

The unicellular eukaryote Paulinella chromatophora possesses an organelle (the cyanelle) which represents an independent case of the acquisition of photosynthesis by cyanobacterial endosymbiosis.


Grouping of Cercozoa.

It has also been described as Sarcomonadea (Cercomonas, Heteromita, Bodomorpha, Proleptomonas, Allantion), Thecofilosea (Cryptodifflugia, Cryothecomonas), Spongomonadea (Spongomonas, Rhipidodendron), and Imbricatea (Thaumatomonas, Thaumatomastix, Allas, Gyromitus, Euglypha, Trinema, Paulinella).


Any eukaryotic organism that is not an animal, plant, or fungus.

Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes

For example, Paramecium bursaria and Paulinella have captured a green alga (Zoochlorella) and a cyanobacterium respectively that act as replacements for chloroplast.