#holobiont

[probablyasocialecologist]

A tiny Hawaiian squid, Euprymna scolopes, has become a model for thinking about this process. The “bob-tailed squid” is known for its light organ, through which it mimics moonlight, hiding its shadow from predators. But juvenile squid do not develop this organ unless they come into contact with one particular species of bacteria, Vibrio fischeri. The squid are not born with these bacteria; they must encounter them in the seawater. Without them, the light organ never develops. But perhaps you think light organs are superfluous. Consider the parasitic wasp Asobara tabida. Females are completely unable to produce eggs without bacteria of the genus Wolbachia. Meanwhile, larvae of the Large Blue butterfly Maculinea arion are unable to survive without being taken in by an ant colony. Even we proudly independent humans are unable to digest our food without helpful bacteria, first gained as we slide out of the birth canal. Ninety percent of the cells in a human body are bacteria. We can’t do without them.

As biologist Scott Gilbert and his colleagues write, “Almost all development may be codevelopment. By codevelopment we refer to the ability of the cells of one species to assist the normal construction of the body of another species.” This insight changes the unit of evolution. Some biologists have begun to speak of the “hologenome theory of evolution,” referring to the complex of organisms and their symbionts as an evolutionary unit: the “holobiont.” They find, for example, that associations between particular bacteria and fruit flies influence fruit fly mating choice, thus shaping the road to the development of a new species. To add the importance of development, Gilbert and his colleagues use the term “symbiopoiesis,” the codevelopment of the holobiont. The term contrasts their findings with an earlier focus on life as internally self-organizing systems, self-formed through “autopoiesis.” “More and more,” they write, “symbiosis appears to be the ‘rule,’ not the exception. . . . Nature may be selecting ‘relationships’ rather than individuals or genomes.”

Anna Lowenhaupt Tsing, The Mushroom at the End of the World: On the Possibility of Life in Capitalist Ruins

[rebeccathenaturalist]

Could Humans Have a Brain Microbiome?

The discovery that other vertebrates have healthy, microbial brains is fueling the still controversial possibility that we might have them a

I'm fascinated by microbiomes, the communities of bacteria, unicellular fungi, and other tiny living beings that populate various parts of animal bodies. We literally can't function without them; our gut micriobiome, for example, is crucial to our ability to digest food.

It's long been thought that the brain was kept sterile by the blood-brain barrier. However, this recent study shows that fish have a brain microbiome, so it's not entirely out of the realm of possibility we might, too. It's tough to study, because accessing the brain opens up the risk of outside contamination confounding the results of the study.

But if it is true, the implications could be huge. There's already a growing body of evidence that our gut microbiome has a significant impact on our mental health and mood through what's known as the Gut-Brain Axis. This is a series of connections between these parts of the body that includes the nervous, endocrine, immune, and other systems. Given there's about one microbial cell for every human cell in our bodies, it wouldn't be at all surprising that our microbial communities have a bigger influence on our lives than we think.

Because it's quite dangerous to study a living human brain, it will be difficult to determine whether we do have cranial microbiomes. But I'll be keeping my eye out for any further news along these lines.

[loneberry]

As biologist Scott Gilbert and his colleagues write, “Almost all development may be codevelopment. By codevelopment we refer to the ability of the cells of one species to assist the normal construction of the body of another species.” This insight changes the unit of evolution. Some biologists have begun to speak of the “hologenome theory of evolution,” referring to the complex of organisms and their symbionts as an evolutionary unit: the “holobiont.” They find, for example, that associations between particular bacteria and fruit flies influence fruit fly mating choice, thus shaping the road to the development of a new species. To add the importance of development, Gilbert and his colleagues use the term “symbiopoiesis,” the codevelopment of the holobiont. The term contrasts their findings with an earlier focus on life as internally self-organizing systems, self-formed through “autopoiesis.” “More and more,” they write, “symbiosis appears to be the ‘rule,’ not the exception…. Nature may be selecting ‘relationships’ rather than individuals or genomes.”  —Anna Lowenhaupt Tsing, The Mushroom at the End of the World: On the Possibility of Life in Capitalist Ruins

[green-algae]

I, holobiont. Are you and your microbes a community or a single entity?

By Derek J Skillings

You yourself are swarming with bacteria, archaea, protists and viruses, and might even be carrying larger organisms such as worms and fungi as well. So are you a holobiont, or are you just part of one? Are you a multispecies entity, made up of some human bits and some microbial bits – or are you just the human bits, with an admittedly fuzzy boundary between yourself and your tiny companions? The future direction of medical science could very well hinge on the answer.

[kenyatta]

The hologenome theory of evolution, also known as the hologenome concept of evolution,[1][2][3] recasts the individual animal or plant (and other multicellular organisms) as a community or a "holobiont" – the host plus all of its symbiotic microbes. Consequently, the collective genomes of the holobiont form a "hologenome". Holobionts and hologenomes are structural entities[4] that replace misnomers in the context of host-microbiota symbioses such as superorganism (i.e., an integrated social unit composed of conspecifics), organ, and metagenome. Variation in the hologenome may encode phenotypic plasticity of the holobiont and can be subject to evolutionary changes caused by selection and drift, if portions of the hologenome are transmitted between generations with reasonable fidelity. One of the important outcomes of recasting the individual as a holobiont subject to evolutionary forces is that genetic variation in the hologenome can be brought about by changes in the host genome and also by changes in the microbiome, including new acquisitions of microbes, horizontal gene transfers, and changes in microbial abundance within hosts. Although there is a rich literature on binary host–microbe symbioses, the hologenome concept distinguishes itself by including the vast symbiotic complexity inherent in many multicellular hosts. 

[rebeccathenaturalist]

Q&A: Holobiont biology, a new concept for exploring how microbiome shapes evolution of visible life

Microorganisms—bacteria, viruses and other tiny life forms—may drive biological variation in visible life as much, if not more, than genetic

Y'all, I am SO excited about this!!!! I've long been fascinated with holobionts, which are basically miniature ecosystems that revolve around one relatively large being essentially acting as a habitat for a whole host of tinier ones in a generally symbiotic relationship. A lichen is (at least to our current understanding) a relatively simple version thereof, with a mycobiont (fungus) creating structure for photobionts (algae and/or cyanobacteria) and, more recently, unicellular yeast--and possibly others we haven't discovered yet.

But our body's microbiomes also make us holobionts! Our skin, guts, and vaginal flora are all a part of our bodies as much as our cells, and often outnumber the human cells in our systems. We are walking around with veritable nations of microscopic beings living out generation after generation in and on our bodies, and without them we would cease to exist. (Though they would outlast us a while in the event of our death.)

What's really cool about this study is that it demonstrates how it's not just our own human genes that shape our evolution, but the ever-changing genomes of our microbiome residents as well. It really pokes holes in the reductionist idea that we are biological islands that grow and develop independently of other beings, and adds a whole new set of layers to us being part of wider, interconnected ecological systems.

We might pretend we're separate from the rest of nature as we build more concrete, steel, and plastic barriers. But we constantly carry our legacy as animals with us, embedded within the matrices of our bodies, just as we carry our heritage of the ocean in our constant need for water and salinity. No matter how much we try to sterilize our indoor environments and our food and our bodies, we are constantly rife with the thriving, overflowing riot of life that has accompanied us from the time our ancient ancestors pasted their split daughter cells together instead of sending them off on their divergent ways.

[kokemoha]

How to be a good Holobiont?

Holobiont in biology refers to “an organism plus its persistent communities of symbionts” (Gilbert 2017: M73) and was used for decades by scientists focusing on plants.

How to be a good Holobiont? Relating during the COVID-19 pandemic by Sabine Biedermann | EASST Review 39(1) 2020

[chanademoura]

Holobiont