To take a quote from Trevor Goward, a fellow Vancouverite nerd, "Lichens are fungi that have discovered agriculture." That's right, humans are not the only farmers on the planet!
Most of you have probably seen lichens before and regarded it simply as a weird crust on a rock. But they are so much more than crust! Lichens are the result of a symbiotic relationship between a fungus (usually ascomycetes, for you super sciencey folks) and a photosynthetic bacteria algae. To further complicate things, recent research suggests that yeasts (which are another, non-ascomycete type of fungus) may also be essential to the survival of most lichens. However, in this article I will focus on the partnership between fungi and bacteria, because I have a particular soft spot in my heart for cyanobacteria.
Cyanobacteria: that's a new word! These amazing bacteria are able to do something that most people think only plants are capable of. They can photosynthesize! You might remember that in the second Microbial Buddies edition, we talked about a symbiosis in which plants provide nutrients for bacteria, via photosynthesis. This week's model symbiosis turns that relationship on its head! This time, it is the bacteria which provide nutrients for a fungus, in the form of sugars made using the power of the sun.
Within the lichen, the cyanobacteria will grow within a firm structure formed by the fungus. You can think of the fungus as the concrete walls of a factory, providing structure and protection for the (bacterial) workers within. Researchers think that the fungal encasement around the cyanobacteria probably provides good protection against UV radiation from the sun and drying out in warm weather. In addition, like any good factory, the fungus also provides the bacteria with good plumbing (a reliable water source). Finally, there is also some evidence that the fungus might provide its bacterial buddy with mineral nutrients that would be more difficult for the bacteria to find on its own.
This intricate living arrangement between the fungus and cyanobacteria seems to provide benefits to both parties, so many scientists call this symbiosis mutualistic. In biological parlance, the word "symbiosis" on its own only means that two organisms are living together - not necessarily in peace. For example, the relationship between these zombie ants and their mind-controlling fungus is also a symbiosis, although not a very useful one for the ant. A mutualistic symbiosis is a more specific term that implies what it sounds like: mutual benefit for both parties!
We'll end this third and final (for now, at least!) edition of the Microbial Buddies series with a little environmental side note. Lichens, these intricately balanced, beautifully peaceful, and startlingly beautiful mutualistic symbioses, are in danger. Lichens are very sensitive to air pollution. In fact, some scientists use the presence of lichens as an indicator of how polluted the air is. The agriculture industry, followed by the transportation industry, are two main contributors to air pollution today – so you can help save the lichens by taking actions like reducing your meat intake and car use.
Until next week, appreciate the lichens under your feet!
- Alex