Like humans, plants and animals, bacteria need food to survive.
Some bacteria are autotrophs, meaning they use basic inputs such as sunlight, water and chemicals from the environment to create food (think cyanobacteria, which have been turning sunlight into oxygen for roughly 2.5 million years) [source: Konhauser et al.]. Other bacteria are what researchers call heterotrophs because they draw energy from existing organic matter for food (think dead leaves on the forest floor).
The truth is, what might be appetizing to bacteria is probably repulsive to us. They've evolved to thrive on all sorts of things, from oil spills and nuclear byproducts to human waste and decaying matter.
But bacteria's penchant for a particular food source can benefit society. For instance, art experts in Italy turned to bacteria to chow down on excess layers of salt and glue threatening the longevity of priceless artwork [source: Asociación RUVID]. Bacteria's knack for recycling organic matter also comes in handy, especially considering their tremendous role as recyclers of the Earth's surface — both in soil and water.
On a daily basis, you might be all too familiar with the odor-inducing effects of hungry bacteria from that funky smell in your trashcan while they take on your leftovers, breaking them down and releasing their own gaseous by-products. It doesn't stop there, though. You also have bacteria to blame for those nature-calling moments (yes, flatulence), when bacteria in your gut release foul-smelling methane during digestion.