[LINK] "The Fuzzy Edges of Life"

[rfmcdonald]

Matt Warren linked to some great stuff about how the ideas of organisms which distinct boundaries and bacteria as unicellular organisms are so limited. Is this biology for the post-modernist?

The number of bacterial species in the human gut is estimated to be about 40,000, according to Daniel Frank and Norman Pace, writing in the January 2008 Current Opinion in Gastroenterology. The total number of individual bacterial cells in the gut is projected to be on the order of 100 trillion, according to Xing Yang and colleagues at the Shanghai Center for Bioinformation Technology, reporting in the June 2009 issue of PLoS One, a peer-reviewed online science journal. Xing calculated a ballpark figure for the number of unique bacterial genes in a human gut at about 9 million.

In fact, most of the life on the planet is probably composed of bacteria. They have been found making a living in Cretaceous-era sediments below the bottom of the ocean and in ice-covered Antarctic lakes, inside volcanoes, miles high in the atmosphere, teeming in the oceans — and within every other life-form on Earth.

[I]n principle, every bacterium can exchange genes with every other bacterium on the planet. A side effect of this reality: The notion of separate bacterial species is somewhat shaky, although the term is still in use for lack of a better alternative.

And bacteria don’t just get together for “file sharing.” Even before quorum sensing was discovered in V. fischeri, scientists had noted many examples of coordinated action, such as “swarming,” in which a colony of bacteria moves as a unit across a surface, and the development of “fruiting bodies,” in which bacteria glom together to form inert spores as a means of surviving severe environmental conditions. Since the dominant paradigm assumed that bacteria were dumb, discrete individuals, these phenomena tended to be glossed over until Vibrio‘s highly sophisticated census-taking focused new attention on coordinated bacterial behavior. Group behavior has now been demonstrated so widely that many microbiologists view bacteria as multicellular organisms, much of whose activity — from gene swapping to swarming to biofilm construction — is mediated by a wide variety of chemical communications.

Giovannoni stops short of claiming that bacteria are actually thinking. But the litany of bacterial talents does nibble at conventional assumptions about thinking: Bacteria can distinguish “self” from “other,” and between their relatives and strangers; they can sense how big a space they’re in; they can move as a unit; they can produce a wide variety of signaling compounds, including at least one human neurotransmitter; they can also engage in numerous mutually beneficial relationships with their host’s cells. Even more impressive, some bacteria, such as Myxococcus xanthus, practice predation in packs, swarming as a group over prey microbes such as E. coli and dissolving their cell walls. (Brown, emphasis mine)