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About Bacterial Growth

Bacteria, which are almost the smallest living organisms in the world (viruses are actually smaller) need certain conditions to grow. They grow in stages and are able to multiply exponentially even in very small areas over a period of hours or days.

  1. Lag Phase

    • The initial lag phase is a period in which growth is slow. During this time, the bacteria become accustomed to the nutrients and food in their new location. When the bacteria do grow, each cell becomes larger and then splits into two cells. Those two cells grow and split as well. This process is called binary fission. Some bacteria prefer cold environments and others grow well in very hot temperatures.

    Log Phase

    • During the log phase, the rate of growth increases tremendously, and the bacteria are able to double their number in just a few minutes. The pH must be ideal for bacteria to grow--typically, between 6.7 and 7.5. (A lower pH means a more acidic environment.) Osmotic pressure is also important to bacterial growth. Since they are 80 to 90 percent water, they need to be in a moist location. They receive the majority of their nutrients from a moist environment.

    Stationary Phase

    • As the number of bacteria increases, the amount of nutrients and food available becomes insufficient. During this phase, the bacterial waste begins to accumulate. As a result, growth slows again and the number of bacteria becomes more fixed, or stationary. Basically, the number of bacteria that die is about the same as the number that grow.

    Death Phase

    • As the food supply continues to dwindle and waste increases, the bacteria start to die. They may decrease in number to a point where only a few bacteria are left, or they may all die. If there are a few surviving, they begin the process over again.

    Bacteria Requirements

    • Bacteria need certain elements in order to survive. Each type of bacteria has specific requirements. Along with water and the correct pH balance, they may need salt, sugar, carbon, nitrogen, hydrogen, phosphorus, sulfur, potassium, iron, calcium and magnesium. Some types of bacteria may also need oxygen or light. Because the conditions must be ideal for growth, it is sometimes difficult for scientists to duplicate the appropriate environment in labs.

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