E. coli (bacteria)
Joy Bhan
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Classification/ Diagnostic Characteristics

E-Coli belongs to the bacteria kingdom as well as the bacterium domain. E-coli is rod-shaped, also referred to as a bacillus. [1]


Domain: Bacteria

Kingdom: Bacteria

Phylum: Proteobacteria

Class: Gamma Proteobacteria

Order: Enterobacteriales

Family: Enterobacteriaceae

Genus: Escherichia

Species: Escherichia coli (E. coli)

Escherichia coli was discovered by Theodor Escherich in 1885 after isolating it from the feces of a newborn. At first, it was described as Bacterium coli commune, but then it was later named Escherichia coli (named for Escherich). It wasn't until 1935, however, that it was found that E. coli was the cause of diarrhea in newborns. [16]

Escherichia coli is one of the many groups of bacteria that live in the intestines of healthy humans and most warm-blooded animals. E. coli bacteria help maintain the balance of normal intestinal flora (bacteria) against harmful bacteria and synthesize or produce some vitamins.There are hundreds of types or strains of E. coli bacteria. Different strains of E. coli have different distinguishing characteristics. [17]

The Gram stain is a technique that separates most types of bacteria into two distinct groups, Gram-positive and Gram-negative. Bacterial cells on a microscope are soaked in violet dye and treated with iodine. It is then washed with alcohol and counterstained with red dye. Gram-positive bacteria retain the violent dye and appear blue to purple. Gram-negative bacteria pick up the red dye counterstain and appear pink to red. [1]


Relationship to humans

E-coli usually reside in the lower intestine of humans. E-Coli is in fact a necessary organism in the human body. It helps with the absorption of Vitamin K and other vitamins in the colon of the human body. E-Coli also immune, digestive, and reproductive health. Vitamins B12 and K are produced by bacteria living in the large intestine. The biofilm that prokaryotes line in the human intestine facilitate nutrient transfer from the intestine into the body. [1]

Although it has may benefits, some serotypes of the E-coli bacterium can lead to serious food poisoning in humans. E-coli is infamous for its ability to infect the intestinal system and causing diarrhea. The diarrhea that the serotype causes can eventually lead the kidney failure which can result in death. Most strains of E. coli are harmless, but 0157:H7, produces a potent toxin - Shiga toxin -that can be harmful to the small intestine. The shiga toxin can also disrupt the function of ribosomes. (7)


Other effects of harmful E-coli serotypes include urinary tract infections and respiratory infections. Transmission of the bacteria is largely through contaminated food and water.[4]





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Serotype 0157:H7


Habitat and niche

The primary habitat of E-coli is within the the intestines of endotherms. The niche of E-coli depends on nutrient availability within the intestine of the host organism. Since the intestines are home to many nutrients, they provide the environment that the E-coli needs to thrive and prosper.

E. coli can live in a variety of nutrient rich environments shown by their usual habitat, the nutrient filled intestines, where their niche is dependent on the closest nutrient. (6)

E. Coli can survive outside of a host for a limited period of time. A growing body of evidence also suggests that E. Coli could be developing strains which could allow it to live for much longer periods of time outside of the body.(15)

Predator avoidance

E-Coli are very motile organism and whenever they detect an issue with their environment, it can either swim away or toward it, depending on what it is.

When in contact with antibiotics trying to seek out and kill the bacteria, some bacterial diseases are evolving into new strains that are resistant to most classes of antibiotics.[1]


Nutrient acquisition

Most of E-coli's nutrient is acquired from it's environment, most commonly being the intestines of an endotherm (warm-blooded organism). Most of the nutrients that e-coli acquires is from the host. Since this organism thrives in an environment that is limiting for many types of nutrients that are required for the cell to grow, E. coli accumulates molecules through a system called solute transporters. Most of these transport systems require energy input from the protons' motor force or ATP hydrolysis. (8)

E. coli have simple nutritional needs, a rapid growth and reproductive rate, and genomic information that is more well-researched and well-documented than any other living organism to date. Therefore, scientists commonly use E. coli as "model organisms", which are used to conduct research pertaining to genetic change, evolution, and other areas that capitalize on the organism's easy maintenance and breeding rate. Researchers have been using E. coli for experimentation since as early as 1988 and are still using it to make advances in science in the contemporary world. (5)

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Reproduction and life cycle

A cell of the bacterium Escherichia Coli (E-coli) is the whole organism, so when it divides to form two [[#|new cells]], it is reproducing. Single-celled prokaryotes like e-coli reproduce through the process of Binary Fission, an asexual process in which the cell grows in size, replicates its DNA, and then separates the cytoplasm and DNA into two new cells. The life cycle of e-coli involves steady cell growth until the cell reaches the beginning of cell division. The cell will then split to produce two identical clones. [1]

E. Coli usually takes about 20 minutes to duplicate. In terms of its life cycle, it has a lag phase (where growth is slow), log phase (where the bacteria multiplies exponentially), stationary phase (where bacteria growth stabilizes), and death phase. (9) (10)


E-Coli Cell in the midst of Reproduction
E-Coli Cell in the midst of Reproduction












Growth and development

Growth and development of Escherichia Coli is determined by the availability of nutrients in its environment. If the E-Coli has proper access to these nutrients, it will steadily grow until it reaches the phase of cell division. The nutrients it receives for proper growth and function. This contributes to the mutualistic relationship that E-Coli has with its host organism.

Optimal growth of E. coli occurs at 37 °C (98.6 °F) but some laboratory strains can multiply at temperatures of up to 49 °C (120.2 °F).[24] Growth can be driven by aerobic or anaerobic respiration, using a large variety of redox pairs, including the oxidation of pyruvic acid, formic acid, hydrogen and amino acids, and the reduction of substrates such as oxygen, nitrate, fumarate, dimethyl sulfoxide andtrimethylamine N-oxide. (11)
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Growth of 1 type of E-Coli Cell





Integument

E-Coli is shielded by a cell wall which acts as the integument. The wall shields the bacterium from any outside intruders/oppressors.

The cell walls of almost all bactera contain peptidoglycan, a cross-linked polymer of amino sugars that produces a meshlike structure around the cell. This is also relative to the Gram stain test. A Gram-negative cell wall usually has a thin peptidoglycan layer, which is surrounded by a second, outer membrane quite distinc in chemical makeup of the plasma membrane.
A Gram-positive cell usually has about 5 times as much peptidoglycan as a Gram-negative cell wall. [1]

Movement

E-Coli are motile organisms that utilize flagella for their movement. In order to reach a specific destination, they utilize their flagella to swim towards it.

Bacterial organisms like Escherichia coli have developed mechanisms that allow them to detect and direct cell movement toward nourishment when starved. Such behavior is known as chemotaxis. When the concentration of the food attractants increases, a signal is transmitted from the chemoreceptors, the chemical receptors, to the flagellar motor, which controls the flagellum and influences the random movement of the bacterium. Only some nutrients, such as specific amino acids and sugars, can be sensed by the chemotaxis signal transduction system, the process that converts a chemical stimulus into a specific cellular response. There are two modes of swimming behavior that are employed by the flagellar motor rotation: counter clockwise rotation, which makes the cell ‘run,’ and clockwise rotation, which makes the cell ‘tumble.’ Both modes are used by Escherichia coli to be as close as possible to nutrient rich environments, with cells being capable of running four times longer than tumbling. (12)





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Sensing the environment

E-Coli do have a sense of touch. It has been tested and results show that they do have surface sensation. (13)

There is a relationship between the bacterial genome and sensing the environment When E. coli senses it's environment through a series of physical and chemical signals, changes in these respective signals, which would be caused by changes in the surrounding physical/chemical environment, alter the gene expression. With lots of changes in the environment happening at once, there is a coordination of multiple response systems. (pg. 373-374) [18]

E-coli sense their environment physical and chemical signals, such as sensing the temperature, or the presence of iron and carbon sources. Environmental changes causes a gene expression change that ultimately helps the e-coli sense its surroundings without a sense of touch. [19]

Gas exchange

E-Coli typically exchanges gas and obtains energy through the process of anaerobic respiration. Since bacteria are in constant contact with their environment, gas exchange typically occurs by diffusion through the plasma membrane.

E. Coli. is a facultative anaerobe, meaning that they can use aerobic respiration or fermentation depending on the current environment. If the presence of oxygen varies, they can switch from one method to the other. [1]


Waste removal

Bacteria such as E-Coli usually have waste products pass directly through their plasma membrane

Environmental physiology (temperature, water and salt regulation)

E-coli survive in temperatures from 40 C - 100 C. However, e-coli prosper most at about 37 C and a neutral pH of ~7. Because its environment is always changing, it can use certain methods to adapt to these changing environments.
Scientists in Munich have recently found two proteins, GroEL and GroES, that have evolved in E-Coli that stabilize folding proteins under stress. This means that these proteins allow E- Coli to thrive in increasingly higher temperatures by preventing internal proteins structures from unfolding at high temperatures. (14)


Internal Circulation

Bacteria such as E-Coli do not possess a complex circulation system. Nutrients can diffuse into the membrane and waste products can be diffused out of the membrane. The nutrients travel throughout the cell. This is because bacterium are so small that they can entirely rely on diffusion for circulation and do not need a circulatory system.

Chemical control (i.e. endocrine system)

E Coli is unicellular, so it has no complex endocrine system. Its chemical control is the result of its cell wall (which keeps the inside of the cell shielded from the outside environment), and its semipermeable membrane.

Review Questions
  1. Explain the process of reproduction for E Coli. Make sure to include binary fission and the four phases in your explanation.
  2. Explain how E. Coli can affect humans both positively ad negatively.
  3. What is the importance of flagella in E.Coli movement, especially in the process of chemotaxis? Make sure to explain thoroughly what chemotaxis is, and why it is important to E.Coli (what does it help E.Coli acquire?).
  4. In what ways are E. Coli useful to humans? What kind of a relationship is that between humans and E. Coli?
  5. Explain how E. Coli, such a simple organism, is able to sense stimuli in its environment.


References

1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.2. Nordqvist, Christian. "What Is E. Coli? (Escherichia Coli)." Medical News Today. MediLexicon International, 08 June 2011. Web. 12 Dec. 2012.3."Bacteria Divide and Multiply." Bacterial Growth and Multiplication. N.p., n.d. Web. 13 Dec. 2012.
4. "E-Coli Infection." Center for Disease Control and Prevenenta. Web. 18 Jul. 2012
5. http://www.emlab.com/s/sampling/env-report-03-2010.html
6. "Escherichia Coli." Escherichia Coli. N.p., n.d. Web. 14 Dec. 2012. http://bioweb.uwlax.edu/bio203/s2008/moder_just/habitat.htm
7. Nordqvist, Christian. "What Is E. Coli? (Escherichia Coli)." Medical News Today. MediLexicon International, 08 June 2011. Web. 14 Dec. 2012.
8. "Nutrient Transport." E. Coli Student Portal. N.p., n.d. Web. 14 Dec. 2012.
9. "Bacteria Divide and Multiply." Bacterial Growth and Multiplication. N.p., n.d. Web. 14 Dec. 2012.
10. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC278050
11. "Escherichia Coli." Wikipedia. Wikimedia Foundation, 14 Dec. 2012. Web. 14 Dec. 2012.
12. Matsuzaki, Yuri. "A Model Library of Bacterial Chemotaxis in the E-Cell System."Landesbioscience.com. N.p., n.d. Web. Dec.-Jan. 2012.
13. Otto, Karen, and Thomas Silhavy. "Surface Sensing and Adhesion of Escherichia Coli Controlled by the Cpx-signaling Pathway." Pnas.com. N.p., n.d. Web. Dec.-Jan. 2012.
14. "Technology Transfer Blog." Scientists Watch as E. Coli Bacteria Evolve Heat Resistance under Stress: New Details of an Evolutionary Mechanism. N.p., n.d. Web. 14 Dec. 2012.
15. Ishii S, Sadowsky MJ (2008). "Escherichia coli in the Environment: Implications for Water Quality and Human Health". Microbes Environ. 23 (2): 101–8.
16."Escherichia Coli." Escherichia Coli. Bioweb.uwlax..edu, n.d. Web. 21 Dec. 2012.
17.http://medicalcenter.osu.edu/patientcare/healthcare_services/infectious_diseases/ecoli/Pages/index.aspx
18.http://books.google.com/books?id=7vFpeDcjBH0C&pg=PA373&lpg=PA373&dq=e+coli+sensing+environment&source=bl&ots=fMWc6Dqa9K&sig=shBqJwAS8NpWc8Jpg7o1YOp0v4A&hl=en&sa=X&ei=TRTOUOPYA8WL0QGYmoCQCQ&ved=0CEcQ6AEwAg#v=onepage&q=e%20coli%20sensing%20environment&f=false
19.http://books.google.com/books?id=7vFpeDcjBH0C&pg=PA373&lpg=PA373&dq=e+coli+sensing+the+environment&source=bl&ots=fMWc9Ct78H&sig=J0NRIQCIqbzgbgEi4DjEoypXco4&hl=en&sa=X&ei=nIvSUJCgBcXZ0QHzjYHoCw&ved=0CE0Q6AEwBA#v=onepage&q=e%20coli%20sensing%20the%20environment&f=false