source: Entangled Life (chapter 3) by Merlin Sheldrake

A handful of lichen species can survive in full space conditions

  • other extreme organisms have been sent to space, but they can’t survive cosmic rays like lichens can

The study of ecology is based on the idea that organisms can’t be understood in isolation

the dual hypothesis of lichens

Swiss botanist Simon Schwendener published a paper on lichens (1869) arguing that lichens aren’t a single organism. They’re composed of:

  • the mycobiont, a fungus that offers physical protection and acquires nutrients
  • the photobiont, an alga that photosynthesizes

Lichens are an example of species converging

  • as opposed to how species diverge, as described in Darwin’s theory of evolution (published 1859)

The German botanist Albert Frank coined the term symbiosis to describe the fungal-algal partnership in lichens (1877)

fungus-algea relationships

reproduction:

  • sometimes they reproduce together
  • sometimes they produce spores that travel alone
  • single fungal spores have to find a compatible photobiont in order to live
  • one in five of all known fungal species will lichenize (form lichens)
    • Some fungi used to lichenize but don’t anymore
    • some fungi can lichenize but don’t have to
  • If you grow many times of free-living fungus and algea together, they’ll develop symbiosis in a matter of days (published in 2014 by Harvard researchers)

Lichen facts!

  • Lichen encrust 8% of the planet’s surface
  • weathering - the (lichen) process of mining minerals from rock
  • when lichens die and decompose, they make the first soil in a new ecosystem
  • The oldest living lichen is 9000 years old (lives in Swedish Lapland)
  • Earliest lichen fossils date back 4 million years
  • Lichens have evolved independently between nine and twelve times since then
  • The first things to grow on barren land is lichens
    • when a volcano creates a new island in the pacific
    • when a glacier retreats

Lichen and panspermia

Panspermia hypothesis that proposes that life arrived on Earth from elsewhere in the universe (not taken seriously by most scientists)

  • soft-panspermia life evolved on Earth, but the chemical building blocks came from space

BIOMEX goal is to find out whether life forms can survive in space

Lichens are extremophiles, and can probably survive in space (there have been several studies)

  • hardy lichens can rehydrate after 24 hours of “space-induced” damage
  • hardy lichens have thick layers of tissue that can block damaging rays
  • can resuscitate after ten years of dehydration
  • lichens are important for the idea of panspermia

Horizontal Gene Transfer

Horizontal gene transfer means that genes are infectious

  • implies a way for branches of the evolutionary tree to converge within organisms

Joshua Lederberg, biologist. won a Nobel Prize for discovering horizontal gene transfer in bacteria

  • raised the concern of celestial contamination in the 1950s
  • Coined the terms exobiology
  • Coined the term microbiome (in 2001)

The Endosymbiotic Theory

states that eukaryotes arose when a single-celled organism engulfed a bacterium

  • mitochondria and chloroplasts are descendants of the engulfed bacteria
  • Lynn Margulis (American biologists) argued the idea (1967)
  • Confirmed in the 1970s by genetic tools
  • we’ve found other examples of endosymbiosis since then

An implication of endosymbiotic theory is that organisms horizontally acquired entire bacteria. This is another example of converging evolutionary branches

Three domains of life

  1. bacteria
  2. archaea - single celled microbes
  3. eukarya - everything else that’s alive

Infra-terrestrials

bacteria and archaea that live kilometers below the planets surface

  • they’re extremophiles, so they prefer intense pressure and heat
  • the subsurface worlds are as diverse as the Amazon rainforest
  • this is over half of all bacteria and archaea on Earth
  • Some specimens are thousands of years old

There are lichens inside chunks of granite, and we have no idea how they got there

This is all according to recent findings from the Deep Carbon Observatory

More partners in lichens

Tony Spribille - lichenologist, hypothesized that lichens might involve additional symbiotic partners

  • did this by grinding up a lichen and sequencing the DNA
  • found four additional organisms, mostly yeast and bacteria
  • this means that lichens are microbiomes

This suggests that lichen symbiosis isn’t as rigid as we thought - lichens are dynamic systems

Now, we haven’t found any lichen that has exactly one fungus and one alga (the traditional idea of a lichen)

Holobionts

A holobiont is an assemblage of different organisms that behave as a unit (holo is “whole” in Greek)

The findings behind lichens imply that all organisms are indistinct from their microbial communities. This includes us

Mammals have microbial populations in our bodies

  • We depend on these symbiotic partners for development
  • We inherited many of our microbes, along with our own DNA

Our mitochondria have their own genome (this is also the case for chloroplasts in plants)

8% of the human genome originated in viruses