Researchers have found several reasons to believe that bacteria affect the mental health of humans. For one thing, bacteria produce some of the same types of neurotransmitters that regulate the function of the human brain. The human intestine contains a network of neurons, and the gut network routinely communicates with the brain. Gut bacteria affect that communication. “The bugs are talking to each other, and they’re talking to their host, and their host talks back,” Young says. The phrase “gut feeling” is probably, literally true.
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For example, 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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“For a long time, these deep sediments were thought to be devoid of any life at all,” he says. There’s life down there, all right, but talk about slow metabolism: When Parke analyzed 4.7 million-year-old organic sediment in the Mediterranean, he estimated the average time it took for resident microbes to reproduce by cell division at 120,000 years. And he reported finding living bacteria just over a mile below the seafloor, in sediments 111 million years old and at temperatures of 140 to 212 degrees Fahrenheit.
These and other new findings suggest that microbes deep in submarine rock may play a heretofore unrecognized role in the regulation of not just the oceans, but the global environment.
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But just how smart are they, really?
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.
The Gut Speaks
Bacteria rule the world in more ways than we know:
