Intelligence is not a quality to attribute lightly to microbes. There is no reason to think that bacteria, slime molds and similar single-cell forms of life have awareness, understanding or other capacities implicit in real intellect. But particularly when these cells commune in great numbers, their startling collective talents for solving problems and controlling their environment emerge. Those behaviors may be genetically encoded into these cells by billions of years of evolution, but in that sense the cells are not so different from robots programmed to respond in sophisticated ways to their environment. If we can speak of artificial intelligence for the latter, perhaps it’s not too outrageous to refer to the underappreciated cellular intelligence of the former.

Under the microscope, the incredible exercise of the cells’ collective intelligence reveals itself with spectacular beauty. Since 1983, Roberto Kolter, a professor of microbiology and immunobiology at Harvard Medical School and co-director of the Microbial Sciences Initiative, has led a laboratory that has studied these phenomena. In more recent years, it has also developed techniques for visualizing them. In the photographic essay book Life at the Edge of Sight: A Photographic Exploration of the Microbial World (Harvard University Press), released in September, Kolter and his co-author, Scott Chimileski, a research fellow and imaging specialist in his lab, offer an appreciation of microorganisms that is both scientific and artistic, and that gives a glimpse of the cellular wonders that are literally underfoot. Imagery from the lab is also on display in the exhibition World in a Drop at the Harvard Museum of Natural History. That display will close in early January but will be followed by a broader exhibition, Microbial Life, scheduled to open in February.

High magnification of the slime mold Physarum polycephalum shows the cytoplasm pumping furiously through its huge single cell. Scott Chimileski/Roberto Kolter This cytoplasmic streaming allows the slime mold to push forward toward nutrients and potentially carpet a surface. Scott Chimileski/Roberto Kolter

The slime mold Physarum polycephalum sometimes barely qualifies as a microorganism at all: When it oozes across the leaf litter of a forest floor during the active, amoeboid stage of its life cycle, it can look like a puddle of yellowish goo between an inch and a meter across. Yet despite its size, Physarum is a huge single cell, with tens of thousands of nuclei floating in an uninterrupted mass of cytoplasm. In this form, Physarum is a superbly efficient hunter. When sensors on its cell membrane detect good sources of nutrients, contractile networks of proteins (closely related to the ones found in human muscle) start pumping streams of cytoplasm in that direction, advancing the slime mold toward what it needs.

But Physarum is not just reflexively surging toward food. As it moves in one direction, signals transmitted throughout the cell discourage it from pushing counterproductively along less promising routes. Moreover, slime molds have evolved a system for essentially mapping their terrain and memorizing where not to go: As they move, they leave a translucent chemical trail behind that tells them which areas are not worth revisiting.