Endosymbioses and Evolution

There is a lot to be gained from attempting to divorce oneself from the past while looking forward at cell biological problems with modern data, and there is clearly much about the evolution of the eukaryotic cell that still needs to be worked out [1].

Scientific definition of the symbiosisThe term “symbiosis”, firstly defined as “the living together of unlike organisms”, is in fact broadly applied to all the spectrum of beneficial, neutral, or harmful relationships [2].

Symbioses include intracellular bacteria in eukaryotic hosts (the core knowledge of ENDOBIOS), which remain largely unseen due to the lack of clear phenotypes and tractable experimental systems [3-6].

Inside the cell: the nucleus and two representative endobacteria

Fast facts on bacteria:

  • It is estimated that 99% of all bacterial species are unculturable, a paradigm known as the great plate count anomaly [7], much related to genome reduction with lack of genes essential for free-living [8].
  • With a global diversity estimated between 100 million to 10 billion species [9], bacteria have an outstanding genetic diversity spread throughout 92 Phyla, with more than half of them remaining without a single culturable representative [10].
  • Unculturable bacteria represent a current major challenge in microbiology [9]. Access to the still neglected bacteria that reside on humans (for example our gut microbiota) and discovering their functionalities is expected to provide new ways to improve health [7].

Fast facts on symbioses: 

  • The first ever found fossil record of Life on Earth were already complex symbiotic communities of bacteria – the stromatolites. Since the oldest known fossil record on Earth – the ca. 3.5 Ga (billion years) old stromatolites from Australia -, prokaryotes are known to co-exist in complex symbiotic communities that engaged in important ecological interactions for billions of years [11].
  • Ancient microbial stromatolitic complexes dominated Life for 80% of Earth’s history [12].

    Present-day stromatolites are rarely found in the planet and must be protected: they are the living fossils of early Life on Earth

    Fossils of ancient stromatolites

  • Intimate symbioses still endure today, e.g. in cyanobacterial hosts and their symbiotic bacteria [13], algae [14] and plants [15].
  • In sponges, the most primitive form of animal life, symbiotic microbes can constitute up to 60% of their biomass [16, 17].

Representation of cyanobacteria, the only bacterial Phylum capable of performing oxygenic photosynthesis (only a fraction of the members of this Phylum), being the templates that originated the eukaryotic chloroplasts. They are directly or indirectly responsible for all the oxygen produced in our planet. Their capacity to generate high amounts of energy makes them the core element present in the ancient symbiotic bacterial communities of stromatolites.

To have a glance on our 10+ years’ experience in the field of endosymbioses, read Almeida et al., 2018 [18]. Importantly, the majority of the ENDOBIOS know-how is yet unpublished.


  1. Archibald, John M., Endosymbiosis and Eukaryotic Cell Evolution. Current Biology 2015, 25, (19), R911-R921.
  2. de Bary, A., Die Erscheinung der Symbiose: Vortrag gehalten auf der Versammlung Deutscher Naturforscher und Aerzte zu Cassel. Trübner: 1879.
  3. Lackner, G.; Partida-Martinez, L. P.; Hertweck, C., Endofungal bacteria as producers of mycotoxins. TIMI Trends in Microbiology 2009, 17, (12), 570-576.
  4. Kobayashi, D. Y.; Crouch, J. A., Bacterial/Fungal interactions: from pathogens to mutualistic endosymbionts. Annual review of phytopathology 2009, 47, 63-82.
  5. Tarkka, M. T.; Sarniguet, A.; Frey-Klett, P., Inter-kingdom encounters: recent advances in molecular bacterium-fungus interactions. Current genetics 2009, 55, (3), 233-43.
  6. Rohm, B.; Scherlach, K.; Mobius, N.; Partida-Martinez, L. P.; Hertweck, C., Toxin production by bacterial endosymbionts of a Rhizopus microsporus strain used for tempe/sufu processing. International journal of food microbiology 2010, 136, (3), 368-71.
  7. Harwani, D., The Great Plate Count Anomaly and the Unculturable Bacteria. Int J Sci Res, 2013, 2, (9), 350-351.
  8. McCutcheon, J. P.; Moran, N. A., Extreme genome reduction in symbiotic bacteria. Nature reviews. Microbiology 2011, 10, (1), 13-26.
  9. Overmann, J.; Abt, B.; Sikorski, J., Present and Future of Culturing Bacteria. Annual Review of Microbiology 2017, 71, (1), 711-730.
  10. Hug, L. A.; Baker, B. J.; Anantharaman, K.; Brown, C. T.; Probst, A. J.; Castelle, C. J.; Butterfield, C. N.; Hernsdorf, A. W.; Amano, Y.; Ise, K.; Suzuki, Y.; Dudek, N.; Relman, D. A.; Finstad, K. M.; Amundson, R.; Thomas, B. C.; Banfield, J. F., A new view of the tree of life. Nature Microbiology 2016, 1, 16048.
  11. Walter, M. R.; Buick, R.; Dunlop, J. S. R., Stromatolites 3,400–3,500 Myr old from the North Pole area, Western Australia. Nature 1980, 284, 443.
  12. Awramik, S. A., Ancient stromatolites and microbial mats. In Microbial Mats: Stromatolites., Cohen Y, C. R., Halvorson HO,, Ed. Alan R. Liss: New York, 1984; pp 1-22.
  13. Alvarenga, D. O.; Fiore, M. F.; Varani, A. M., A Metagenomic Approach to Cyanobacterial Genomics. Frontiers in microbiology 2017, 8, 809.
  14. Sambles, C.; Moore, K.; Lux, T. M.; Jones, K.; Littlejohn, G. R.; Gouveia, J. D.; Aves, S. J.; Studholme, D. J.; Lee, R.; Love, J., Metagenomic analysis of the complex microbial consortium associated with cultures of the oil‐rich alga Botryococcus braunii. MicrobiologyOpen 2017, 6, (4), e00482.
  15. Akinsanya, M. A.; Goh, J. K.; Lim, S. P.; Ting, A. S. Y., Metagenomics study of endophytic bacteria in Aloe vera using next-generation technology. Genomics Data 2015, 6, 159-163.
  16. Mohamed, N. M.; Rao, V.; Hamann, M. T.; Kelly, M.; Hill, R. T., Monitoring bacterial diversity of the marine sponge Ircinia strobilina upon transfer into aquaculture. Applied and environmental microbiology 2008, 74, (13), 4133-43.
  17. Webster, N. S.; Thomas, T., The Sponge Hologenome. mBio 2016, 7, (2), e00135-16.
  18. Almeida, C., et al., Appl Environ Microbiol, 2018. 84, 15, e00660-18