Growth and Physiology of Prokaryotic Cells

Binary fission is a simple form of asexual reproduction seen in prokaryotes.2 The circular chromosome attaches to the cell wall and replicates while the cell continues to grow in size. Eventually, the plasma membrane and cell wall begin to grow inward along the midline of the cell to produce two identical daughter cells. Because binary fission requires fewer events than mitosis, it can proceed more rapidly. In fact, some strains of E. coli can replicate every 20 minutes under ideal growth conditions.2

Binary_fission
Binary Fission

 

One of the biggest challenges a doctor faces is that of patient compliance with treatment, especially antibiotics. Many patients fail to complete an entire course of antibiotics, often discontinuing the treatment because they feel better. Unfortunately, this breeds antibiotic resistance by killing off the bacteria that are non-resistant and leaving behind bacteria that are more resistant. These resistant bacteria then reproduce, resulting in recurrence of the infection. Over time, this practice has led to bacteria that are resistant to multiple antibiotics, making common infections more difficult to treat.

As discussed previously, bacteria reproduce by binary fission. This implies that all of the bacteria are exactly the same in a local colony (assuming no mutations or genetic recombination), and no bacteria will be dividing faster than the others. Bacteria can be said to grow in a series of phases. In a new environment, the bacteria first adapt to the new local conditions during the lag phase.2 As the bacteria adapt, growth increases, causing an exponential increase in the number of bacteria in the colony during the exponential phase, which can also be called the log phase. As the number of bacteria in the colony grows, resources are often reduced. The reduction of resources slows reproduction, and the stationary phase results. After the bacteria have exceeded the ability of the environment to support the number of bacteria, a death phase occurs as resources in the environment have been depleted.

lag-log-stationary-death-phases
Source: https://courses.lumenlearning.com/microbiology/chapter/how-microbes-grow/

 

Oxygen is needed for some bacteria to survive while others do not need it. Obligate aerobes refer to bacteria that need oxygen to carry out metabolic function. Anaerobes are the bacteria that make use of the process of fermentation, or non-oxygenic cellular metabolism. Anaerobes that cannot survive in an oxygen-containing environment are called obligate anaerobes and the presence of oxygen leads to the production of reactive oxygen-containing radicals in these species, which leads to cell death.2 There are species of bacteria can switch between either metabolic processes. They can utilise oxygen for aerobic metabolism if necessary and are able to carry out anaerobic metabolism as well. These bacteria are referred to as facultative anaerobes. Aerotolerant anaerobes are bacteria which are unable to use oxygen for cellular metabolism, but, unlike obligate anaerobes, they are not harmed by its presence in the environment.

In a parasitic relationship, the bacteria benefits at the expense of the host. Disease causing bacteria are examples of parasitic relationships. For the mutualistic relationship, both bacteria and host benefits. The commensalistic relationship is where one party benefits while the other has no effect.

 

References

1) Villarreal, L. P. (2008, August 8). Are Viruses Alive. Scientific American.

2) Campbell, N. (2003). Biology:Concepts & Connections. San Francisco: Pearson Education.

3) Sinkovics, J., J, H., & A, H. (1998). he Origin and evolution of viruses (a review). Acta Microbiologica et Immunologica Hungarica, 349 – 390.

4) Crick FH, W. J. (1956). Structure of small viruses. Nature, 473- 475.

5) Boevink P, O. K. (2005). Virus-host interactions during movement processes. Plant Physiology, 1815–21.

6)  NC State University. “Prokaryotes: Single-celled Organisms

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