Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: Francis Tapon on 08/07/2011 03:01:02

Title: Are there organisms that eat rocks?
Post by: Francis Tapon on 08/07/2011 03:01:02

Francis Tapon  asked the Naked Scientists:
   
Chris,

Me and my vegetarians friends can get smug about our "ethical" eating habits, but we're still killing living things to survive. It seems that all life needs to eat other life to live. Is that true?

Or are there organisms that can eat rocks and steel to survive?

The only example I can think of are the extremophiles that live by ocean vents, eating chemicals that spew out of the vents (assuming those chemicals are non-living organisms). Plants survive on photosynthesis, but perhaps they need to eat microbacteria to grow.

Are there more exotic examples you can think of?

Francis Tapon

What do you think?

Title: Are there organisms that eat rocks?
Post by: richboden on 07/07/2011 18:23:24

Organisms that eat rocks are known as lithotrophs ("rock eaters") and are mostly Bacteria and Archaea but also some fungi. They "eat" rock in that they use metals and inorganic ions present in the rock as an energy source and then use this energy to take up carbon dioxide from the air (or dissolved in water) - just like plants do but plants gain the energy they need from light rather than from inorganic ions. A lot of lithotrophs use inorganic sulfur compounds in the rock (such as sulfide or polythionates) as energy sources and produce sulfuric acid as their waste product. This is excreted from the cells and can dissolve carbonates in rocks like limestone, which in turn can release metal ions, making them available as energy source, but, more importantly, releases carbon dioxide, which the bacteria can then consume. This is the process by which a type of cave known as a "karst" is formed - the acid secreted by the bacteria is what slowly dissolves the limestock rock making the cave bigger. These bacteria aren't usually extremophiles - Thiobacillus spp. are an example and they can be found pretty much everywhere - on most rock surfaces but also on concrete and even bricks, as well as on and in our bodies! Examples such as Halothiobacillus are salt-tollerant but not to really extreme levels. Others tollerate higher salt and heat and so are true extremophiles. The ones in the vents you mention are just the same. My research focuses on lithotrophic organisms in a karst in Romania - you can find out more at my website: http://www.richboden.com (http://www.richboden.com).

So, these organisms don't eat other organisms to survive - they use inorganic chemicals and carbon dioxide. Sometimes, that carbon dioxide can come from that formed by other organisms - so you can think of them as getting their carbon from something's breath! Other bacteria can use methane ("methanotrophs") as their carbon and energy source and this is often produced geologically rather than from the fossil fuel route so they don't need to eat other organisms to survive either.

Whilst some bacteria need other life to survive (Mycobacterium and Mycoplasma spring to mind) and some can even directly eat other bacterial cells, a huge number of those in the environment just consume chemicals in soils such as acetate that are produced by Archaea as waste products but they aren't actually eating other life - they're living off of the waste products of it. Much like the Bacteria in our feces!

Hope that answers your question a bit!
rich

Title: Are there organisms that eat rocks?
Post by: CliffordK on 07/07/2011 21:01:00

If you go to a volcano (lava flow or pumice flow), you will find trees and other plants growing where no plants have grown before, and I believe the volcanic ash is rich in inorganic minerals that the plants use.

Lichens also "eat rock".  However, lichens use symbiosis.  Does that count?

Oxygen, Water, CO₂, and etc are all recycled through living tissue, but not always involving death.

If you eat peas or flour, you are actually eating fertilized plant seeds...  is there anything worse than eating the young of a species?  When you eat an apple, you don't eat the seeds, but you often discard them just the same.  However, fruit is designed as a seed distribution system and is intended to be eaten.

Title: Are there organisms that eat rocks?
Post by: Airthumbs on 08/07/2011 01:36:07

Some slightly larger organisms eat rocks, Crocodiles, Birds, Seals and many others, they are commonly known as Gastroliths.  These organisms do not necessarily digest the rocks but use them to aid in digestion.  Technically they are eating them though.  [;D]

This link will give you more information about this if your interested http://www.ucmp.berkeley.edu/taxa/verts/archosaurs/gastroliths.php