A colorized electron microscope image captures delicate chains of streptococcus in a laboratory sample. Though some strep infections can be deadly, many strains are harmless—among the thousands of benign beings that make their home in our bodies.
Photograph by Department of Microbiology, Biozentrum, University of Basel/Photo Researchers, Inc
All Images Colorized
These bacteria-infecting viruses, phages for short, are the most abundant life-form on the planet, their number far exceeding that of stars in the universe. Trillions inhabit each of us.
The common waterborne bacterium Caulobacter crescentus reproduces asymmetrically. When a cell divides, one of its daughter cells is a free-swimming “swarmer,” powered by a hairlike flagellum. The other, “stalk” daughter cell is immobile, anchoring itself to a surface with one of nature’s strongest glues, resisting five tons of force per square inch.
Photograph by Dennis Kunkel Microscopy, Inc
PHAGES IN ACTION
Bacteriophages escape from a dying streptococcus bacterium, ready to find another victim. Their ability to infect and kill specific strains may lead to new treatments for antibiotic-resistant bacteria.
The human gut teems with bacteria, many of their species still unknown. They help us digest food and absorb nutrients, and they play a part in protecting our intestinal walls. Gut bacteria may also help regulate weight and ward off autoimmune diseases.
Helicobacter pylori (yellow), a common bacterium that lives in the stomach lining, increases the risk of stomach cancer (brown cells) and peptic ulcers. But over time H. pylori can reduce stomach acid and acid reflux, which may help fend off esophageal cancer. The microbe also appears to help protect us from allergies and asthma. Some scientists suspect that the dramatic increase in those conditions in the industrialized world could be related to the decreasing frequency of H. pylori in our stomachs, which is partly due to high doses of antibiotics in childhood.
Photograph by Eshel Ben-Jacob and Inna Brainis
A lab-grown colony of Paenibacillus vortex organizes into a fanlike pattern, with arms reaching out to scout for food. Bacteria can act collectively, communicating with chemical signals.
Photograph by Steve Gschmeissner, Photo Researchers, Inc
Tiny green cyanobacteria played an outsize role in Earth’s history by creating the planet’s oxygen-rich atmosphere through photosynthesis. Ancestral forms also evolved into chloroplasts, the cell parts that carry out photosynthesis in plants.
The human mouth hosts a panoply of microbes, some taking up residence on the mouth lining (blue) within days after birth. Harmful species form biofilms, like the plaque that encourages tooth decay, or colonize the crevices between teeth and gums, causing periodontal disease. Oral probiotics designed to boost the population of species that outcompete pathogenic ones could help prevent or reverse dental disease.
The bug lives harmlessly in the noses of about a third of us. But it can turn rogue, causing skin infections—or worse. Heavy use of antibiotics since the middle of the last century has prompted the evolution of deadly superbug strains.