Bacteria are tiny, one-celled organisms-- generally 4/100,000 of an inch wide (1 micron) and somewhat longer in length. What bacteria lack in size, they make up in numbers. We can't avoid them. The air around us is teeming with them. With every breath we take, we inhale thousands of bacteria, viruses and fungi. A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria. That is as much mass as two cows per acre. 1