Sentient Slime?

Research Blogging / by Dave Munger /

Slime molds form patterns similar to rail and road networks, and bacteria organize slimy scouting parties and move in groups. Is there such a thing as microbial intelligence?

Slime molds are some of the most curious organisms known to science. They can be both multicellular and unicellular, which means they can survive as single-celled amoeba-like creatures, but they can also pool together into larger groupings to act as a single organism. When two single-celled slime molds meet, they can merge, sharing a cell membrane. Eventually they can become quite large, even stretching over a meter in length, composed of thousands of cell nuclei but with no membranes separating them into individual cells. Other slime molds are more like tiny slugs that crawl around until they find food.

The patterns of their motion can be fascinating, and sometimes even appear to exhibit intelligence. When the slime mold Physarum polycephalum locates food, it leaves a slender tendril to that source while it expands its search to find more. “Hannah,” a recent graduate who works in a Philadelphia molecular biology lab, uncovered two studies comparing P. Polychephalum networks to human traffic networks.

In 2009, University of West England, Bristol researchers Andrew Adamatzky and Jeff Jones placed food on a damp coffee filter in a Petri dish in a pattern corresponding to the major cities of Great Britain. The filter paper itself was cut to match the shape of Great Britain’s island. Then they placed the P. Polychephalum on the food source corresponding to London, and observed the movements of the slime mold as it grew. The networks formed by the slime mold closely matched major roads of Britain. Their research was published in the International Journal of Bifurcation and Chaos.

This year, a team led by Atsushi Tero replicated those results, generating a slime-mold map of the Tokyo rail system. Does this mean slime molds are “intelligent?” Probably not; a likelier explanation is that they simply have evolved an efficient means to transport food, similar to the patterns intelligent humans create for their own transport.

But slime molds aren’t the only simple organisms that seem to team up for the good of the group. A post on the anonymous blog “geek!” discusses research uncovering similar “social networking” in the bacteria responsible for African sleeping sickness. These single-celled parasites were previously thought to be independent, moving through the blood of their hosts propelled by tail-like flagella. But in a study published last month in PLoS Pathogens, a team led by UCLA’s Michael Oberholzer found that the bacteria, T. brucei, moves in clumps across the agar in a Petri dish. There were even specialized “scout” cells that sought out others to join the group and directed the clump around obstacles.

Another human pathogen, H. pylori, is remarkable in a different way. It’s one of the few bacteria able to withstand the highly acidic conditions in the human stomach. H. pylori is present in nearly half of all humans, and is responsible for a wide array of ailments, most notably peptic ulcers and some forms of acid reflux. But Tim Sampson, a graduate student in microbiology and molecular genetics, notes that researchers have only recently learned how H. pylori gets through the extremely thick mucus lining our stomachs.

It’s well established that H. pylori excretes ammonia to neutralize stomach acid, but a team led by Jonathan P. Celli of Boston University showed that the ammonia is useful not just for neutralizing acid, but also makes the stomach lining less viscous and elastic. Celli’s team cleverly used a dye that glows at more neutral pH levels, and found that as the mucus becomes less acidic, it also becomes more liquid, allowing the H. pylori to penetrate the mucus and colonize the gastric pits below, where it thrives and reproduces with a nearly infinite food supply and no competition from other bacteria.

While the ingenious strategies “simple” organisms use to move around may not be indications of human-level intelligence, they do make it abundantly clear that organisms like bacteria and slime molds are no “less evolved” than humans. Scientists are constantly uncovering amazing evolutionary sophistication in the unlikeliest of places. As new discoveries are made, look for additional commentary and discussion on

Originally published February 24, 2010

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