Bacteria are everywhere. They are one of the main groups of organisms that cause disease. But there are also many that are very beneficial. All bacteria are capable of rapid growth and have distinct growth stages. Most can survive in an environment regardless of whether or not oxygen is available--some must have oxygen, while others cannot exist with it.
Bacterial Reproduction
Bacteria reproduce by a process called binary fission. It is asexual reproduction because it does not involve two sexes. Instead, one bacterial cell divides in half to form two cells. This process is also referred to as exponential growth because one cell leads to two cells, then each of those two will divide to give a total of four cells, and so on. Thus, in just three generations, one bacterium becomes eight bacteria.
Different bacteria have different reproduction times. E. coli can reproduce in 20 minutes, while M. tuberculosis takes 24 hours, for example. So in just seven hours, one E. coli can become one million, according to the book, "Review of Medical Microbiology and Immunology."
Stages of Growth Cycle
There are four stages in the growth cycle of bacteria. The first stage is called the lag phase. During this stage, bacteria prepare the environment for their growth. They get rid of any toxins and turn on their enzymes. This stage can last for just a few minutes or several hours. The logarithmic phase, also called the exponential phase, is the second stage of growth. Bacteria reproduce by binary fission during this stage. The third stage is referred to as the stationary phase. All of the nutrients that the bacteria need have now been used up, and toxic products start to accumulate. As a result, bacterial growth now slows. The number of new bacteria will equal the number that died. According to "Jawetz, Melnick, & Adelberg's Medical Microbiology," when bacteria are grown in a special environment where nutrients are added and waste products are removed before they become toxic, the bacteria will stay in the logarithmic stage. The death stage is the fourth and final stage, where bacteria have a sharp decrease in their numbers.
Obligate Anaerobes
There are two enzymes bacteria use to grow in an environment that has oxygen. The obligate anaerobes are missing one or both of these enzymes. These bacteria, therefore, cannot grow in an environment where there is oxygen, and must grow in an anaerobic environment, or an environment where there is no oxygen. Some of the obligate anaerobes will die in an aerobic environment. Others may be able to survive, but they will not be able to grow. The "Review of Medical Microbiology and Immunology" notes that Clostridium tetani is an example of an obligate anaerobe.
Facultative Anaerobes
This group of bacteria can grow in an environment whether it has oxygen or not. If there is oxygen, they will be able to use that oxygen to successfully grow. If there is no oxygen, they will be able to get their energy in a different way. Most bacteria are facultative anaerobes.
Obligate Aerobes
Obligate aerobes must have oxygen in their environment to be able to grow. They have both of the enzymes that they need to use oxygen for energy. M. tuberculosis is an obligate aerobe, according to the "Review of Medical Microbiology and Immunology."
References
- "Jawetz, Melnick, & Adelberg's Medical Microbiology"; George Brooks, M.D., Karen Carroll, M.D., Janet Butel, Ph.D., Stephen Morse, Ph.D.; 2007
- "Review of Medical Microbiology and Immunology"; Warren Levinson, M.D., Ph.D.; 2008
