Holobiont

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The holobiont or the entire organism is a biological system that consists of a eukaryotic host organism and a plurality of prokaryotic species that live closely together with this. The expression holobiont is composed of Greek elements: Hólos <όλος> everything, whole, whole; bíos <βίος> life; óntos <όντος> Being, being. The word was introduced in 1991 by the biologist Lynn Margulis .

Current research in the life sciences suggests that all eukaryotes with them beneficial prokaryotes (bacteria and archaea ), possibly including the viruses, a community form, often even depend on them. The symbiotic functional way of life is not to be understood as an exception, but as a general requirement. Holobionts are therefore multi-part ecological units. The genome of the holobiont consists of the genomes of the host and its symbionts, i.e. of several genomes; it is also known as a hologenoma. To call a holobiont a metaorganism expresses that a microbiome exists in connection with the large organism, often inside it, for example in the digestive tract : its peculiar microbe complex. Species of the microbiome can also exist as free-living organisms and can each be individually absorbed from the environment. Often, however, it is a matter of specialized symbionts that no longer occur apart from their host and are no longer viable on their own. In the course of a symbiogenesis , this close living community can progress to the integration of the symbiont in its host organism.

The term “holobiont” contains the interaction of different species, which distinguishes it from the term “ superorganism ”, in which individuals of the same species live together. Example: bee colony ; its individuals also have their own microbiome.

New insight

To see the large living beings with their population of bacteria and viruses as a whole has been known in individual cases for a long time, but its universal distribution has become clear through the techniques of advanced DNA sequencing . This makes the individual genome components visible in hologenomes: The phylogenetic development of plants and animals was probably dependent on symbiosis with microorganisms. The majority of bacteria and viruses are rarely harmful; they are much more likely to help shape or at least modulate anatomy and physiology .

The mammals are no exception in the respect described. Humans are also holobionts. Its microbiome influences, for example, the nervous system and personal individuality. Anyone born through vaginal birth received their microbiome from their mother, namely strains of Actinobacteria and Bacteroidia . However, the predominant clostridia in the maternal intestine have not been observed in babies. Caesarean section babies can receive their maternal microbiome as an initial supply via a vaginal smear .

Mammals with an extremely one-sided diet are absolutely dependent on the help of their microbiome. A dramatic example are the vampire bats , which only consume blood. Its dry matter consists of 93% protein and only about 1% carbohydrates . The extensive investigations on the common vampire found attention in quality journalism. Similar communities are also known from other haematophagous animal species. They are widespread in species with one-sided composite food substrates and can consist of numerous species. The community in the rectum of the wood-eating termites has been well researched.

Models of the holobiosis

Delisea pulchra , also synonymous: D. japonica - National Museum of Nature and Science, Tokyo
Microfoto of the freshwater polyp: Hydra viridissima

In order to find out the how and why of the entire organisms, observations and experiments on simply built eukaryotes, which are also easy to keep in the laboratory, are recommended. Sponges meet such conditions.

Caulerpa taxifolia is an introduced and therefore unpopular green alga in the Mediterranean. Both the alga and its symbiotic bacteria vary little. The limited hologenoma is responsible for the decline in the Mediterranean. It is different in southern Australia, where this holobiont lives due to its varied genetic composition. The metabolism of the bacteria promotes adaptability and competitiveness of the consortium.

The red Delisea pulchra grows off the coasts of Australia and Japan . For the first time, bacteriophages and other virus particles appeared in this large alga in the transmission electron microscope . Sequencing of the nucleic acids revealed groups of viruses with double-stranded RNA belonging to the genus totivirus . In addition, a virus with single-stranded RNA from the order Picornavirales was identified.

Initial studies on the microbiome of Sphagnum found methanotrophic, phototrophic and nitrogen-binding bacteria, from whose metabolic products the peat moss benefits as a host. Such research is ecologically important because sphagnum is an important repository for carbon worldwide, especially in northern peat systems. The moss is suitable as a model for experiments because it also grows under laboratory conditions.

Among the Hydrozoen the coming Hydra to the forefront. Your glycocalyx and mucous membrane are a chemical-physical barrier that houses microbes. This part of the microbiome is interrelated with the polyp. Unusual fungal infections result when Hydra lacks the bacteria. Another handicap was found in sterile polyps: their otherwise regular pulsing gets out of step, the pulse frequency decreases

literature

  • Ricardo Guerrero, Lynn Margulis, Mercedes Berlanga: Symbiogenesis: The holobiont as a unit of evolution. In: Int Microbiol 16 (3), 2013: 133-143.
  • Peter Kramer, Paola Bressan: Humans as superorganisms: How microbes, viruses, imprinted genes, and other selfish entities shape our behavior . In: Perspectives on Psychological Science 10 (4), 2015: 464–481. doi: 10.1177 / 1745691615583131.
  • Lauren A Richardson: Evolving as a holobiont. In: PloS Biol 15 (2), 2017: e2002168. PMC 5330447 (free full text)
  • Deborah CA Leite, Joana F Salles, Emiliano N Calderon, Jan D van Elsas, Raquel S Peixoto: Specific plasmid patterns and high rates of bacterial co-occurrence within the coral holobiont. In: Ecology and Evolution 8, 2018: 1818-1832. PMC 5792611 (free full text)
  • Suhelen Egan, Tilmann Harder, Catherine Burke, Peter Steinberg, Staffan Kjelleberg, Torsten Thomas: The seaweed holobiont: Understanding seaweed – bacteria interactions. In: FEMS Microbiology Reviews 37 (3), 2013: 462-476. doi : 10.1111 / 1574-6976.12011

Individual evidence

  1. ↑ Lynn Margulis in: Lynn Margulis, René Fester (Ed.): Symbiosis as a source of evolutionary innovation: Speciation and morphogenesis. MIT Press, Cambridge MA 1991, ISBN 978-0-262-51990-8 .
  2. ↑ Eugene Rosenberg, Gil Sharon, Ilil Atad, Ilana Zilber-Rosenberg: The evolution of animals and plants via symbiosis with microorganisms. In: Environmental Microbiology Reports 2 (4), 2010: 500-506. doi: 10.1111 / j.1758-2229.2010.00177.x .
  3. ^ P Kundu, E Blacher, E Elinav, S Pettersson: Our gut microbiome: The evolving inner self. In: Cell 171 (7), 2017: 1481-1493. doi: 10.1016 / j.cell.2017.11.024 .
  4. ↑ Katri Korpela, Paul Costea, Luis Pedro Coelho, Stefanie Kandels-Lewis, Gonneke Willemsen, Dorret I Boomsma, Nicola Segata, Peer Bork: Selective maternal seeding and environment shape the human gut microbiome. In: Genome Res gr.233940.117. Advance publication March 1, 2018. doi: 10.1101 / gr.233940.117 . PDF.
  5. ^ M Lisandra Zepeda-Mendoza et al. (29 authors): Hologenomic adaptations underlying the evolution of sanguivory in the common vampire bat. In: Nature Ecology and Evolution 2018 (online before print, open access) doi: 10.1038 / s41559-018-0476-8 , PDF 12 pages.
  6. ↑ Fritz Habekuss: Dracula's Diet: Vampire bats feed exclusively on the blood of their host animals. In: Die Zeit 10, March 1, 2018: p. 36.
  7. ↑ Lucia Pita, Sebastian Fraune, Ute Hentschel: Emerging sponge models of animal-microbe symbioses. In: Front Microbiol 7, 2016: 2102-2110. PMC 5179597 (free full text)
  8. ↑ Sophie Arnaud-Haond, T Aires, R Candeias, SJL Teixeira, Carlos M Duarte, M Valero, Ester A Serrão: Entangled fates of holobiont genomes during invasion: Nested bacterial and host diversities in Caulerpa taxifolia. In: Mol Ecol 26 (8), 2017: 2379-2391. doi: 10.1111 / mec.14030
  9. ↑ Tim Lachnit, Torsten Thomas, Peter Steinberg: Expanding our understanding of the seaweed holobiont: RNA viruses of the red alga Delisea pulchra. In: Front Microbiol 6, 2016: 1489. PMC 4705237 (free full text)
  10. ↑ Joel E Kostka, David J Weston, Jennifer B Glass, Erik A Lilleskov, A Jonathan Shaw, Merritt R Turetsky: The Sphagnum microbiome: New insights from an ancient plant lineage. In: New Phytologist 211 (1), 2016: doi: 10.1111 / nph.13993 .
  11. ^ Katja Schröder, Thomas CG Bosch: The Origin of Mucosal Immunity: Lessons from the holobiont Hydra. In: mBio 7 (6), 2016: e01184-16. PMC 5090036 (free full text).
  12. ^ Thomas C Bosch: Understanding complex host-microbe interactions in Hydra. In: Gut Microbes 3 (4), 2012: 345-351. PMC PMC3463492 (free full text)
  13. ↑ Andrea P Murillo-Rincon, Alexander Klimovich, Eileen Pemöller, Jan Taubenheim, Benedikt Mortzfeld, René Augustin, Thomas CG Bosch: Spontaneous body contractions are modulated by the microbiome of Hydra. In: Scientific Reports 7 (1), 2017: 15937. PMC 5698334 (free full text)

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