Definition of bacteria

Bacteria are single-celled microorganisms that are found in virtually every environment on Earth, including soil, water, air, and living organisms. They are among the most ancient and diverse forms of life on the planet, with an estimated 10 million different species. Bacteria are prokaryotes, which means that they lack a true nucleus and other membrane-bound organelles. Instead, their genetic material is contained in a single circular molecule of DNA located in the cytoplasm. Bacteria play important roles in a variety of biological processes, including nutrient cycling, decomposition, and symbiosis with other organisms. Some bacteria can cause disease in humans and other animals, while others are beneficial and are used in industry, agriculture, and medicine.