Vertical transmission

Vertical transmission of symbionts is the transfer of a microbial symbiont from the parent directly to the offspring.[1]  Many metazoan species carry symbiotic bacteria which play a mutualistic, commensal, or parasitic role.[1]  A symbiont is acquired by a host via horizontal, vertical, or mixed transmission.[2]

Implications

Complex interdependence occurs between host and symbiont.[3] The genetic pool of the symbiont is generally smaller and more subject to genetic drift.[4] In true vertical transmission, the evolutionary outcomes of the host and symbiont are linked.[5] If there is mixed transmission, new genetic material may be introduced.[6] Generally, symbionts settle into specific niches and can even transfer part of their genome into the host nucleus.[7]

Evolutionary consequences

Benefits

The mechanism promotes tightly coupled evolutionary pressure, which causes the host and symbiont to function as a holobiont.[8]

Disadvantages

Evolutionary bottlenecks lead to less symbiont diversity, and thus resilience.  Similarly, this greatly reduces the effective population size. Ultimately, without an influx of new genetic material, the population becomes clonal.  Mutations tend to persist in symbionts and build up over time.[9]

Transmission Modes

Germline

Since the egg contributes the organelles and has more space and opportunity for intracellular symbionts to be passed to subsequent generations, it is a very common method of vertical transmission.[1]  Intracellular symbionts can migrate from the bacteriocyte to the ovaries and become incorporated in germ cells.[10]

Live birth

Human infants acquire their microbiome from their mothers, from every sphere where there is contact.  This includes potentially the mother's vagina, gastrointestinal tract, skin, mouth and breastmilk.[11] These routes are typical if the delivery is a vaginal birth and the infant is nursed. When other actions, such as Caesarian delivery, bottle feeding, or maternal antibiotics during nursing occur, these modes of vertical transmission are disrupted.[12][13]

Patrilineal

Though extremely rare, Rickettsia is transmitted to Nephotettix cincticep through the paternal line in the sperm.[14]

Aposymbiotic

Earthworms (Eisenia) have an extracellular symbiont, Verminephrobacter. Rather than being passed through the egg in the germline, the young are aposymbiotic when still in the egg capsule; however, they acquire Verminephrobacter before the egg capsule ruptures, so it is still vertical transmission.[15]

Well studied archetypes

Pea aphids and Buchnera

Pea Aphids do not get all of the necessary amino acids from their diet.  Buchnera, synthesize the needed ones in an obligate relationship.[10]   

Head lice and Candidatus Riesia pediculicola

The head louse (Pediculus humanus)  has an obligate symbiotic relationship with Candidatus Riesia pediculicola.  The louse provides shelter and protection while bacteria provides essential B vitamins. C. riesia lives in the bacteriocyte but move to the ovaries to be transmitted to the next generation.[16]

References
  1. Bright, Monika; Bulgheresi, Silvia (March 2010). "A complex journey: transmission of microbial symbionts". Nature Reviews Microbiology. 8 (3): 218–230. doi:10.1038/nrmicro2262. ISSN 1740-1534. PMC 2967712. PMID 20157340.
  2. Koga, Ryuichi; Bennett, Gordon M.; Cryan, Jason R.; Moran, Nancy A. (2013). "Evolutionary replacement of obligate symbionts in an ancient and diverse insect lineage". Environmental Microbiology. 15 (7): 2073–2081. doi:10.1111/1462-2920.12121. ISSN 1462-2920. PMID 23574391.
  3. Perotti, M. Alejandra; Clarke, Heather K.; Turner, Bryan D.; Braig, Henk R. (2006-09-28). "Rickettsia as obligate and mycetomic bacteria". The FASEB Journal. 20 (13): 2372–2374. doi:10.1096/fj.06-5870fje. ISSN 0892-6638. PMID 17012243.
  4. Wernegreen, J. J.; Moran, N. A. (1999-01-01). "Evidence for genetic drift in endosymbionts (Buchnera): analyses of protein-coding genes". Molecular Biology and Evolution. 16 (1): 83–97. doi:10.1093/oxfordjournals.molbev.a026040. ISSN 0737-4038. PMID 10331254.
  5. Vautrin, Emilie; Vavre, Fabrice (2009-03-01). "Interactions between vertically transmitted symbionts: cooperation or conflict?". Trends in Microbiology. 17 (3): 95–99. doi:10.1016/j.tim.2008.12.002. ISSN 0966-842X. PMID 19230673.
  6. Quigley, Kate M.; Warner, Patricia A.; Bay, Line K.; Willis, Bette L. (December 2018). "Unexpected mixed-mode transmission and moderate genetic regulation of Symbiodinium communities in a brooding coral". Heredity. 121 (6): 524–536. doi:10.1038/s41437-018-0059-0. ISSN 1365-2540. PMC 6221883. PMID 29453423.
  7. Kleine, Tatjana; Maier, Uwe G.; Leister, Dario (2009). "DNA Transfer from Organelles to the Nucleus: The Idiosyncratic Genetics of Endosymbiosis". Annual Review of Plant Biology. 60 (1): 115–138. doi:10.1146/annurev.arplant.043008.092119. PMID 19014347.
  8. Morris, J. Jeffrey (2018-10-19). "What is the hologenome concept of evolution?". F1000Research. 7: 1664. doi:10.12688/f1000research.14385.1. ISSN 2046-1402. PMC 6198262. PMID 30410727.
  9. Smith, Noel H.; Gordon, Stephen V.; de la Rua-Domenech, Ricardo; Clifton-Hadley, Richard S.; Hewinson, R. Glyn (September 2006). "Bottlenecks and broomsticks: the molecular evolution of Mycobacterium bovis". Nature Reviews Microbiology. 4 (9): 670–681. doi:10.1038/nrmicro1472. ISSN 1740-1534. PMID 16912712.
  10. Simonet, Pierre; Gaget, Karen; Balmand, Séverine; Ribeiro Lopes, Mélanie; Parisot, Nicolas; Buhler, Kurt; Duport, Gabrielle; Vulsteke, Veerle; Febvay, Gérard; Heddi, Abdelaziz; Charles, Hubert (2018-02-20). "Bacteriocyte cell death in the pea aphid/ Buchnera symbiotic system". Proceedings of the National Academy of Sciences. 115 (8): E1819–E1828. doi:10.1073/pnas.1720237115. ISSN 0027-8424. PMC 5828623. PMID 29432146.
  11. Bäckhed, Fredrik; Roswall, Josefine; Peng, Yangqing; Feng, Qiang; Jia, Huijue; Kovatcheva-Datchary, Petia; Li, Yin; Xia, Yan; Xie, Hailiang; Zhong, Huanzi; Khan, Muhammad Tanweer (May 2015). "Dynamics and Stabilization of the Human Gut Microbiome during the First Year of Life". Cell Host & Microbe. 17 (5): 690–703. doi:10.1016/j.chom.2015.04.004. PMID 25974306.
  12. Cox, Laura M.; Yamanishi, Shingo; Sohn, Jiho; Alekseyenko, Alexander V.; Leung, Jacqueline M.; Cho, Ilseung; Kim, Sungheon G.; Li, Huilin; Gao, Zhan; Mahana, Douglas; Zárate Rodriguez, Jorge G. (August 2014). "Altering the Intestinal Microbiota during a Critical Developmental Window Has Lasting Metabolic Consequences". Cell. 158 (4): 705–721. doi:10.1016/j.cell.2014.05.052. PMC 4134513. PMID 25126780.
  13. Dominguez-Bello, Maria G.; Costello, Elizabeth K.; Contreras, Monica; Magris, Magda; Hidalgo, Glida; Fierer, Noah; Knight, Rob (2010-06-29). "Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns". Proceedings of the National Academy of Sciences of the United States of America. 107 (26): 11971–11975. Bibcode:2010PNAS..10711971D. doi:10.1073/pnas.1002601107. ISSN 1091-6490. PMC 2900693. PMID 20566857.
  14. Watanabe, K.; Yukuhiro, F.; Matsuura, Y.; Fukatsu, T.; Noda, H. (2014-05-20). "Intrasperm vertical symbiont transmission". Proceedings of the National Academy of Sciences. 111 (20): 7433–7437. Bibcode:2014PNAS..111.7433W. doi:10.1073/pnas.1402476111. ISSN 0027-8424. PMC 4034255. PMID 24799707.
  15. Davidson, Seana K.; Stahl, David A. (2006-01-01). "Transmission of Nephridial Bacteria of the Earthworm Eisenia fetida". Applied and Environmental Microbiology. 72 (1): 769–775. doi:10.1128/AEM.72.1.769-775.2006. ISSN 0099-2240. PMC 1352274. PMID 16391117.
  16. Sasaki-Fukatsu, Kayoko; Koga, Ryuichi; Nikoh, Naruo; Yoshizawa, Kazunori; Kasai, Shinji; Mihara, Minoru; Kobayashi, Mutsuo; Tomita, Takashi; Fukatsu, Takema (2006-11-01). "Symbiotic Bacteria Associated with Stomach Discs of Human Lice". Applied and Environmental Microbiology. 72 (11): 7349–7352. doi:10.1128/AEM.01429-06. ISSN 0099-2240. PMC 1636134. PMID 16950915.
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