Question

how are bacteria useful to us??

Answer 1

Some bacteria degrade organic compounds for energy, and without bacteria, the earth would have no soil in which to grow plants. Bacteria living in the gut can help animals break down food. These so-called 'good bacteria' help maintain the conditions necessary for food digestion.
hope it helps

Answer 2

Bacteria are sometimes useful for us as they decompose every piece of waste. Without them earth would be a giant piece of undecaying waste. Gud bacteria present in Yogurt helps in maintaining Metabolism and health. Last but not the least.. Bacteria could be the pioneer for the future tech that does not cause pollution as they form methane while decomposing waste which could be used to fuel future engines.