Bacteria have no mouth or lungs. The bacteria called Geobacter swallows organic waste and exhale electrons which generates a tiny electric current in the process, according to a September 19 2020 article by Live Science.
Nikhil Malvankar, an assistant professor at Yale University's Microbial Science Institute in Connecticut, told Live Science that Geobacter are 100,000 times smaller than the width of a human hair, but by breathing through a snorkel they trasmit electrons hundreds to thousands of times the length of their body (1).
An August 20 2020 article by Science magazine says Dr. Lars Peter Nielsen of Aarhus University, Denmark, found bacteria that join cells end to end to build electrical cables able to carry current up to 5 centimeters through mud (2).
Theoretically, this suggests that it might be possible to manipulate bacteria to create enough microbe-generated energy for consumer use, as in a "microbe-battery". TBD.