Thursday, June 05, 2008

Evolution: what are microbes?

Once biology terminology breaks out into the world of popular press, the sense of a word is often lost or misconstrued, or never well understood in the first place by either communicator or recipient.

Soon I hope to dive into the sordid mess of genetic terminology. Right now, it's microbes.

Microbe is simply a synonym for micro-organism, or microscopic organism. However, therein lies a welter of misinformation; much of the time, it's rendered synonymous with bacteria - but that's only part of the story. Here is a list - not necessarily complete - of microbes.

Bacteria. Domain: Bacteria - yes, they're a whole grouping unto themselves, which animals, plants and fungi are not, being of domain eukaryote. Bacteria are unicellular with no nucleus (thus prokaryotic). They reproduce by binary fission. There are ten times as many bacteria cells in the human body as human cells, although as prokaryotes they are an order of magnitude or so smaller than human cells.

Archaea: Domain: Archaea. Also prokaryote, reproducing by binary fission. It was thought until relatively recently that they were restricted to extremophilia - that is, only living at the extremes of tolerable ranges of temperature, acidity, etc. Since then, they've been found to be far more common. Possibly the most ancient lineage (hence the name), although there's whole worlds of debate in that issue.

Protists: a paraphyletic grouping (a Kingdom), ie a bucket for things that don't belong together, but don't fit elsewhere. They include unicellular animals (protozoa), plants (protophyta), and fungi (slime molds, water molds).

Amoebae: or amoebas, also lumped in with protists, ie Domain: eukaryota; Kingdom: Protista; phylum: sarcodina. Unicellular.

Algae: again paraphyletic. United by their focus on photosynthesis, they can be either unicellular or multicellular. Cyanobacteria was once called blue-green algae, but this is not accurate.

Plankton: Not a grouping per se, but actually defined by their ecological niche: pelagic (nearer surface) oceans. They encompass animal, plant, bacteria, etc. The bottom of the ocean food chain, and what all other pelagic animals feed on - a mixed diet, but uniformly microscopic.

Virus: Don't really belong here, as they're not classified as living: just bags of DNA seeking hosts, and which cannot live without those hosts. There are viruses for every type of living organism, including those for bacteria (bacteriophages).

Interestingly, genetic information infiltrates and is exchanged in all sorts of ways between these and other, larger organisms. That's quite a story in itself, and hopefully will be tackled soon.

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