Ike’s comin’ right for us, so I don’t know when the my power and internet access will die, and if so how long it’ll be before it comes back. However, while I’m still connected I wanted to contribute something again to this month’s The Giant’s Shoulders blog carnival. Since it’s in three days and there’s a chance our power might be out when the deadline passes, I figured I’d better hurry. Because of the hurry there are no fancy graphics nor even too much explanatory text here, but I’ll do what I can. Fortunately, the basics of today’s post isn’t too complex.
Depending on how rigorous your biology education was, there are a variety of ways that you might tend to categorize the fundamental types of living things. You might vaguely recall something about “five kingdoms”, which as I recall were “Animals, Plants, Fungi, Protozoa [e.g. amoeba], and Bacteria”. You might just segregate everything into either “animal” or “plant”. If your memory of biology education is a bit stronger, you might remember that “bacteria” are a separate group from the true plants and animals. A step more precise and you may split living things into the two domains of “prokaryote” and “eukaryote”.
The “plant” and “animal” distinction is pretty classic – until comparatively recently, bacteria were assumed to be “plants”, just as fungi (“plants” that lacked chlorophyll) were. Non-photosynthetic bacteria were referred to as “schizomycetes” (literally “fission” [splitting in two] fungi, because they reproduce by splitting from one cell into two rather than forming spores), while bacteria with chlorophyll (cyanobacteria or “blue-green” algae, and possibly the “green sulfur bacteria”) were designated “schizophyta” (“fission plants”).
Within the last fifty years or so, though, it’s become obvious that bacteria were a different type of life from fungi, chlorophyll-containing plants, or animals. The latter critters have cells that in turn contain “organelles”, which are more or less very specialized “mini-cells” within themselves. The nucleus, for example, is a compartment within the cell where the cell’s DNA is kept and processed. Bacteria, it turned out, don’t have any of these organelles (in fact there’s good evidence that at least some if not all organelles used to be bacteria, but this post’s long enough already so I won’t go into that), and life was re-organized into the bacterial “prokaryotes” (“before nucleus”) and the “eukaryotes” (having a “true nucleus” – i.e. everything that isn’t bacteria).
Then, along comes Carl Woese, who spoils this nice simple dichotomy. In 1977, he published (along with G.E. Fox) the subject of today’s post:
Continue reading Phylogenetic structure of the prokaryotic domain: the primary kingdoms.
