"We step on soil every day, but few people realize that 'dirt' supports a complex community of microorganisms that plays a critical role on Earth, he said. "The number of bacterial species in a spoonful of soil is likely to exceed the total number of plant species in all of the United States."
We don't have to go traipsing about the garden to appreciate the ubiquity and diversity of bacteria. The typical human body has about 100 trillion cells, but only about 50 trillion of these are 'us' in that they started from our original egg and contain our genome. The rest, making up over half our cells, are an extensive menagerie of critters, mostly bacteria. We are not individuals. We are walking ecosystems. Most of these co-critters serve functions that are useful or even essential for our survival. And of course we serve functions that are essential to their survival.
Lynn Margulis, in her delicious book: "Garden of Microbial Delights" describes this in detail and suggests that perhaps the bacteria are the Intelligent Designers that evolved the so called higher animals like us humans just so they would have a nice temperature stabilized and constant moisture environment and also have someone to bring home the bacon.