Because of there small size and they reproduce every 15 minutes and they can protect themselves in unfavorable conditions
3 4 3
Bacteria are very small organisms consisting of only one cell, they lack chloroplasts too. Bacterial are found everywhere is air,soil, water and even inside our body and our skin.They tend to multiply very rapidly under favourable conditions. Bacteria are prokaryotic cells i.e, cells that don't have a well defined nucleus. Therefore they can live anywhere on the earth.
3 4 3