What is the large family of bacteria that is commonly found in soil and water?

The correct answer is Bacillus. This family of bacteria is known for being commonly found in soil and water environments. Bacillus species are characterized by their ability to form enduring spores, which allow them to survive in difficult conditions. This characteristic not only aids in their persistence in the environment but also plays a crucial role in their application in various biotechnological and agricultural practices.

The other families listed are not primarily known for their prevalence in soil and water. Staphylococcus, for instance, is typically associated with skin infections and is more commonly found in human-associated environments rather than natural ecosystems. Mycobacterium is a group known for its role in diseases like tuberculosis and leprosy, and, while some species can be found in water, they are not broadly distributed in soil and water like Bacillus. E. coli, although largely studied in microbiology and commonly found in the intestines of warm-blooded organisms, is not part of the soil and water bacterium family like Bacillus.