Bacteria 'R' Us - 0 views
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Regardless of the scale at which we explore the biosphere — whether we delve into the global ocean or the internal seas of individual organisms — bacteria are now known to be larger players than humans ever imagined.
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Strictly by the numbers, the vast majority — estimated by many scientists at 90 percent — of the cells in what you think of as your body are actually bacteria, not human cells.
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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.
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For the purposes of this article, we’ll focus on the fundamental difference between two major types of life-forms: those that have a cell wall but few or no internal subdivisions, and those that possess cells containing a nucleus, mitochondria, chloroplasts and other smaller substructures, or organelles.
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The former life-forms — often termed prokaryotes — include bacteria and the most ancient of Earth’s life-forms, the archaea.
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The tree-of-life notion remains a reasonable fit for the eukaryotes, but emerging knowledge about bacteria suggests that the micro-biosphere is much more like a web, with information of all kinds, including genes, traveling in all directions simultaneously.
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In 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.
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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.
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Bacteria can live solitary lives, of course, but they prefer to aggregate in biofilms, also known as “slime cities.” Biofilms usually form on a surface, whether it’s the inner lining of the intestines or inside water pipes or on your teeth. In these close-knit colonies, bacteria coordinate group production of a slimy translucent coating and fibers called “curli” and “pili” that attach the colony to something else. Biofilms can harbor multiple types of bacteria as well as fungi and protists (microscopic eukaryotes). A complex vascular system for transporting nutrients and chemical signals through a biofilm may also develop. As Tim Friend described in his book The Third Domain, explorers diving to the wreck of the Titanic found these features in “rusticles” — draped colonies of microbes — feeding on the iron in the Titanic‘s hull and skeleton, more than 2 miles under the surface.
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The import of this distribution of microorganisms is unclear, but its existence reinforces the notion that humans should start thinking of themselves as ecosystems, rather than discrete individuals.
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A microbe’s effects on the human body can depend on conditions. And if you approach the human body as an ecosystem, some researchers are finding, it may be possible to tune that system and prevent many diseases — from acute infections to chronic debilitating conditions — and even to foster mental health, through bacteria.
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in practice, the medical notion of friendly microbes has yet to extend much past the idea that eating yogurt is good for you. For most doctors and medical microbiologists, microbes are enemies in a permanent war. Medicine certainly has good reason to view microbes as dangerous, since the germ theory of disease and the subsequent development of antibiotics are two of medical science’s greatest accomplishments.
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When threatened, bacteria become defensive, often producing toxins that make the host even sicker. They also tend to speed up their acquisition of and purging of genes when under external selection pressure, of which antibiotics are an obvious and powerful example.
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bacteria produce some of the same types of neurotransmitters that regulate the function of the human brain.
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it’s been known for a while that sick people get depressed and anxious. This seems so obvious as to be a no-brainer, but research suggests that some of the fear and fatigue associated with infections stems from immune responses affecting the brain.
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As it turns out, however, very few bacteria can be grown in the relatively austere conditions of laboratories. In fact, only about 0.1 percent of all bacteria are currently culturable. Many bacteria don’t do well in monoculture, preferring to live in mixed communities of microorganisms. Those living in extreme temperatures and pressures require very specialized equipment to grow in a typical lab.
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In fact, they wrote, the genes that enable these processes today “may have been distributed across a common global gene pool, before cellular differentiation and vertical genetic transmission evolved as we know it today.”
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In other words, bacteria are supreme code monkeys that probably perfected the packages of genes and the regulation necessary to produce just about every form of life, trading genetic information among themselves long before there was anything resembling a eukaryotic cell, let alone the masters of the universe that humans believe humans to be.
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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.
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These phenomena, Herbert Levine’s group argues, reveal a capacity for language long considered unique to humans.
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That bacteria-centric argument is, of course, a hazy, metaphysical Gaian fantasy worthy of Avatar. In a more down-to-earth assessment, it is clear that bacteria are not what the general run of humans thought they were, and neither are humans.
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The grand story of human exceptionalism — the idea that humans are separate from and superior to everything else in the biosphere — has taken a terminal blow from the new knowledge about bacteria. Whether humanity decides to sanctify them in some way or merely admire them and learn what they’re really doing, there’s no going back.