Microbial “Trojan horses” stages

Ingested, but not digested.
Stages: 1) A unicellular organism, or protist, uses hairlike cilia to push assorted bacteria into its oral groove. Ingested bacteria are collected in food vacuoles— specialized organelles, or cellular compartments, where bacteria are exposed to acidic conditions and digestive enzymes.
2) Bacteria are killed and broken down in the food vacuoles, supplying protists with energy and nutrients. But some bacteria (stained green) can release molecules that interfere with the normal digestion process.
3) Digestion-resistant bacteria can survive within unicellular organisms or even reproduce within them.
4) Digestion-resistant bacteria, including some that can cause diseases in humans, can be released back into the environment. (Illustration by Jack Cook, © Woods Hole Oceanographic Institution)