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How many bacteria can the world support?

  1. Nov 2, 2011 #1
    The title says all I'm asking. Thank you.
  2. jcsd
  3. Nov 2, 2011 #2

    jim mcnamara

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    Staff: Mentor

    The short answer is: nobody knows, and it is very unlikely that anything really reliable, unlike the exercise below, will be available any time soon.

    'A Natural History of Subterranean Life' by David W. Wolfe

    A large percentage of the total Earth's biomass is found beneath the surface, mostly as
    bacteria-like organisms [per Wolfe]. Biomass estimates for above ground biomass vary a lot, however, for fun and a way to make a wild guess let's use 56 billion metric tons of fixed carbon. For above ground biomass.

    Since this is just a fun exercise, not real Science, let's also assume that 20% of the biomass above ground is 'bacterial' however that gets defined.... In the same vein, we can use 56 billion tons as the amount of fixed carbon in subterranean life.

    So we have 56 * .20 = 11.2 billion tons (above ground) + 56 billion tons (subterranean) , so our total is 67.2 billion tons.

    So you can get a grip on what we're doing: your body has about one trillion cells in it,
    and let's pretend you weigh 150 pounds. That means we can guess that 1 pound of you is: 1 trillion / 150. This comes out close to 660,000,000,000 cells. (that's 660 billion, the US billion)

    So, let's pretend that our cells and bacterial cells are similar in size and mass (which is not a great assumption). Therefore, to get an really rough idea of the number of bacteria and their relatives on Earth now, multiply 660,000,000,000 * 672,000,000,000.

    I should also mention that some of your biomass is bacteria, e.g., about 10% of the volume of your colon is bacteria and other primitive organisms.

    Also note that what we are calling bacteria here are really a whole range of living one-celled things from primitive algae to organisms that metabolize metals like manganese, to what you probably think of as germs.
  4. Nov 2, 2011 #3


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    IIRC we carry about 1kg of bacteria. There are far more bacteria than human cells in our body with far more genetic material than our genome;
  5. Nov 3, 2011 #4
    How about we start off with Earth.:smile:
    Proc. Natl. Acad. Sci. USA
    Vol. 95, pp. 6578–6583, June 1998
    Prokaryotes: The unseen majority
    William B. Whitman*†, David C. Coleman‡, and William J. Wiebe§
    Departments of *Microbiology, ‡Ecology, and §Marine Sciences, University of Georgia, Athens GA 30602

    ScienceDaily reported the article as well entitled First-Ever Scientific Estimate Of Total Bacteria On Earth Shows Far Greater Numbers Than Ever Known Before:
    Last edited: Nov 3, 2011
  6. Nov 7, 2011 #5


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    Staff: Mentor

    Off topic posts deleted. Thread closed.
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