You are currently inhaling fungi. Fungi are extraordinarily abundant and found almost everywhere around us. It is present in the soil, on our skin, in the food we eat and drifting through the air. Don’t worry, it has been like this for a billion years now.
Most fungi are multicellular; some are unicellular like yeast. The abundant aerial presence of fungi comes from spores, the tiny single cells that serve as their primary method of reproduction. Spores are only one of several routes fungi use to multiply; unicellular fungi reproduce by budding and multicellular fungi reproduce by fragmentation of the mycelium. The mycelium is the main body of most fungi which is a network of thread-like filaments, called hyphae. To release their spores, some fungi build up internal hydraulic pressure in a specialized sac-like structure called sporangia and launch these spores that can be ten thousand times faster than a space shuttle. Fungal spores are the largest source of living particles in the air. Every year around fifty megatons of spores are produced by fungi. So, it should come as no surprise that these fungal spores are found even in the clouds. Fungi thrive in the most unexpected and inhospitable environments where life seems impossible.
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High speed (3,000 fps) video recording of synchronized spore launch. Credit: Dr. M Roper, Dr. A Seminara, et al., “Dispersal of fungal spores on a cooperatively generated wind”
It is the remarkable fungal biology, which allows their mind-blowing abundance and adaptability.
The fungal kingdom
We tend to split the macroscopic living world into two familiar kingdoms, plants and animals. Fungi fall in neither of them and make a third kingdom of their own.
Let’s start with how they eat and derive their nutrients. Plants make their own food using carbon dioxide and water in the presence of sunlight, and animals eat existing living things. In a way, fungus eats all other living things too but digests it before consuming it, unlike animals. While animals swallow their meals to digest it within their bodies, fungi secrete digestive enzymes into their surrounding environment, breaking down complex organic matter externally before absorbing the dissolved nutrients. This extracellular digestion offers a distinct advantage to eat anything that can be broken down.
Furthermore, fungi can also thrive in the high-radiation environment of Chernobyl, by using radiation as a source of energy. Cladosporium sphaerospermum is one of the several species of radiotrophic fungi that uses the pigment melanin to convert radiation into chemical energy. While animals can only consume what physically fits into their mouths or closed guts, fungi do not have such boundaries.
The biologist Merlin Sheldrake writes in Entangled Life, fungi are capable of “eating rock, making soil, digesting pollutants, nourishing and killing plants, surviving in space, inducing visions, producing food, making medicines, manipulating animal behaviour, and influencing the composition of Earth’s atmosphere.”
Fungi exhibit extraordinary behaviours that showcase their unique resilience and power over other living beings. They produce psychoactive compounds like psilocybin that temporarily alter the neural architecture and induce ego dissolution. They can act as behavioral puppeteers, such as the Ophiocordyceps unilateralis fungus which hijacks and controls ants to precisely optimize spore dispersal. They produce antibiotics through natural territory-defending chemical weapons like penicillin, and they possess an unmatched ability to survive global catastrophes, even becoming the dominant life form on land by feasting on dead biomass during the devastating Permian mass extinction.
Interesting right? These just scratch the surface on fungal abilities, but already point that fungi are built to thrive. But the real puzzle appears the moment we ask how fungi do what they do.
How do fungi keep up ?
Micro-organisms are known for their adaptability. Bacteria and viruses adapt at frightening speeds because of their faster reproduction rates. This not only enables them to exist in astronomical numbers but also allows more chances of evolution. These microbes have simpler cellular structures than ours. Viruses are nothing more than a tiny genetic code wrapped in a protein coat, and bacteria are single celled organisms that lack nucleus. This minimal design allows them to replicate at a much faster rate. Each time they divide, they have a chance to change their genes just a little bit. All these changes lead to evolution of newer abilities in them, making them the ultimate shape shifters.
By this logic, fungi should not be able to keep up. They are eukaryotes, with the same fundamental cell design as our own, with a nucleus inside which holds an intricate genome, and an internal machinery of thousands of different proteins and molecular systems that must all be coordinated, and the ability to grow into multicellular bodies. In short, these are complex cells, and complexity normally comes at a cost.
Bigger genomes are slower and riskier to change, and complex organisms usually evolve far more sluggishly than bacteria and viruses. Evolution plays no favourites but large animals like us reproduce slowly and in relatively smaller numbers. These mean a lesser number of diverse individuals. Hence, we get only a handful of rolls of the evolutionary dice each century. That means, if a calamity strikes, we fare or fail quite similarly as compared to the prokaryotes. But not fungi!
Fungi colonise the harshest places on the planet and adapt like the bacteria and viruses. Cryomyces antarcticus can survive in freezing temperatures and ionizing UV radiations, Hortaea werneckii can survive in hypersaline environments etc. The answer to how fungi achieve faster adaptation lies in three tricks.
The number game
The first is brute statistics behind natural selection – the nature’s process of keeping what survives. At its core, natural selection is pure probability. All living organisms are born with small differences in their genetic makeup. These differences can give rise to a new trait and if these new traits help in survival are propagated via reproduction. Over generations, a population fills up with what works. This is the game bacteria win by sheer numbers, and fungi play it just as hard.
A single fungus can release billions of tiny reproductive spores every single day, with a single mushroom fruiting body capable of launching over 30,000 spores per second, multiple times a day. This totals to billions per day. Each of these spores is a slightly different genetic variant, scattered like lottery tickets for survival. From the moment a spore lands on a viable surface and starts to grow, it takes only a matter of 2 to 10 days for it to mature into a complete fungal body ready to reproduce all over again. Enormous numbers multiplied by rapid turnover give fungi bacteria-like evolutionary odds, even though their cells are anything but simple.
The two speed genome
The second trick is built into the genome itself. Fungal DNA is unusually rich in transposons, or “jumping genes”: short stretches of DNA that can copy themselves and paste the copy elsewhere in the genome. These mobile elements are present in almost all living things and are not unique to fungi. What is unusual is how fungi organise and deploy them.
In a fungal cell, transposons are clustered in a specific genomic region. The region goes through a mix of new combinations of genes due to transposon activity. Biologists call this a “two speed genome” where one is a safe zone in the genome that is stable, and another an experimental zone where these jumping genes cluster. The transposons-rich regions get rearranged far faster than the rest of the genome. When a fungus meets a new threat, accidental variations introduced by transposons can happen to act as a fresh defence mechanism. This is like every reshuffle of the transposons is another roll of the dice on those genes generating new variants of genes while the core machinery of the cell stays safe and left untouched.
The pressure test
The third trick is the most elegant, wherein a built-in switch releases hidden variations on demand, governed by dysfunctioning of a protein called Heat shock protein 90 (Hsp90).
Every cell, when it divides, steadily picks up small mutations in its DNA, many are close to neutral: they nudge a protein’s shape only slightly without breaking its function, or they alter behaviour only under conditions the organism has not yet encountered. Such variants are neither clearly good nor clearly bad for the organism, and in a stable environment they just ride along, invisible. Hsp90 is a robust molecular chaperone. When a mutation leaves a certain set of proteins such as the kinases and transcription factors malformed, Hsp90 still bends it into a functional shape.
By bending these slightly malformed proteins back into functional shapes, Hsp90 ensures the organism looks and develops normally, masking the secret variations in its DNA. However, when the environment turns harsh due to heat, toxins, and starvation, Hsp90 is overwhelmed by the demand to fix stress-damaged proteins and can no longer mask the mutations it was hiding. These variations are exposed, and some of the altered protein shapes can turn out to be advantageous in the new stressful conditions.
In the thick of life through changing times
Fungi are complex eukaryotes that keep pace with changing environments. Their strategy is simple – it experiments more to find ways to thrive faster. Their molecular machinery of proteins and regulators is designed to perform trial and error without messing up their core genomes. This has helped them live through changing times and climates.
The oldest fossils widely accepted as fungi such as Ourasphaira giraldae, recovered from Arctic Canada. They are roughly a billion years old, meaning fungi were already remaking the planet long before the first animals crawled onto land. Roughly 155,000 fungal species have been described, but the estimates put the true number between 2.2 to 3.8 million. This means we have so far identified perhaps only one fungus in twenty. And, these millions of fungal species are vital for the survival of the entire biosphere.
With their ability to digest almost anything, fungi serve as the planet’s premier cleanup crew. By decomposing incredibly tough materials like lignin and cellulose, they prevent dead forests from piling up, releasing trapped carbon, nitrogen, and phosphorus back into the soil to nourish the next generation of life. This generosity extends beneath the surface, where the underground mycorrhizal networks connect with the root systems of over 90% of land plants, helping them to survive. By wrapping around plant roots to share nutrients, these ancient survivors prove that their ultimate adaptation is not just about their own endurance but to sustain the network of life.
