Some bacteria that can help the environment are called decomposers. They are "nature's recyclers"! They return basic chemicals to the environment for living things to reuse! For example, the leaves of many trees die in the Autumn and drop to the ground. Then Decomposer bacteria spend the next months breaking down the chemicals in the died leaves. The broken-down chemicals mix with the soil and then can be absorbed by the roots of nearby plants!
As autotrophic bacteria use the sun's energy to produce food, they also release oxygen into the air. As you may know, there was little oxygen in earth's atmosphere billions of years ago. Scientists think that autotrophic bacteria were responsible for firs adding oxygen to Earth's atmosphere. Today the distant offspring of those bacteria help keep oxygen levels in the air stable.
The activities of helpful bacteria produce all kinds of food. For example, bacteria that grow in apple cider change the cider to vinegar. Bacteria that grow in milk produce dairy products such as buttermilk, yogurt, sour cream, and cheese. However some bacteria cause food to spoil when they break down the food's chemicals. spoiled food usually smells or tastes foul and can make you very sick.