E.Coli


 * E.Coli** **By: Louis Yoo**

**1. Classification:** **Kingdom: Bacteria** **Phylum: Proteobacteria** **Class: Gamma Proteobacteria** **Order: Enterobacteriales** **Family: Enterobacteriaceae** **Genus: Escherichia** **Species: Escherichia Coli** **E. coli is a unicellular bacterium, or more specifically, a prokaryote. A prokaryote is defined as a unicellular microorganism that lacks a membrane bound nucleus. Bacteria come in different shapes and sizes, but E.Coli are strictly rod shaped.As a bacterium, E.coli contains few large intracellular( inside cell) structure, and is bound by a lipid (plasma) membrane. E.coli are known for their residence in the lower intestines of warm blooded organisms, and are cause disruption in the food industry for contaminating food supply with a variety of diseases. The flagellum, or hair shaped structures protruding from the outside of the cell membrane are used to propel the bacteria with a whip like motion.**

**2. Relationship to Humans:** **E.coli forms a mutual relationship with its host. The host provides a safe, protected environment with sufficient nutrients for growth. E.coli is essential to the absorption of important vitamins in the body.** **E. Coli is normal flora of the human gut, introduced there in infant-hood through food or other people. While in the gut, E. Coli produces vitamin K2 for the human host and can prevent the establishment of harmful bacteria. Some strains of E. Coli can cause food poisoning in humans, or in the case of more virulent types: gastroenteritis, urinary tract infections, or neonatal meningitis.** **The particular strain of bacteria that causes detrimental effects on the body is known as E. Coli O157:H7 which causes a severe intestinal infection. This strain is the most commonly found within the infections and actually originates from the intestines of healthy cattle. The symptoms can start to show from 2 to 5 days after the digestion of the contaminated food and may last up to 8 days. The questionable factor about diagnosing E. coli is that sometimes the symptoms are not visible or don't correlate with the most common symptoms. It is differentiated from the good E.coli bacteria in the intestines by the potent toxin that is excreted which damages the lining of the stomach tissue and causes things such as: bloody diarrhea, abdominal cramps, nausea, and hemolytic uremic syndrome (which is a severe complication that can lead to kidney failure and ultimate death). E.coli is usually tested for using DNA fingerprinting via stool samples and is compared with a source or contaminated food.**

**E. coli O157:H7 is a strand of E. coli that can produce the harmful Shiga toxin. Similar to the E. coli O157:H7 other strains can produce the shiga toxin they are called STEC. Unlike the O157 strand many non-O157 infections may go undiagnosed or unreported. As a whole, the non-O157 serogroup is less likely to cause severe illness than E. coli O157; however, some non-O157 STEC serogroups can cause the most severe manifestations of STEC illness.**

**E. Coli is widely used in molecular biology. It can be used as a host to produce heterogeneous proteins, and in a larger scales has been used to mass-produce useful proteins such as insulin. E. Coli is also used as a laboratory model organism, and is the primary organism to study for bacterial conjugation. E. Coli has been used by humans in various industrial processes. For one, E. Coli are able to decompose phytic acid into phosphate, which can be used with radioactive waste, binding with uranium to form a precipitate that can be reused to create more nuclear energy in nuclear power plants. Additionally, E. Coli can be used to clean up radioactive waste sites and lower the amount of uranium needed to be mined to fuel nuclear power plants around the world as a type of bioremedition.** **A famous ongoing experiment with E. Coli has provided evidence for evolutionary biology. Since 1988, researchers of the E. Coli Long-Term Evolution Experiment have observed the same populations of E. Coli, alternatively suspending and allowing them to live in gel-glucose media. They observed that fitness initially increased, then leveled off. The experiment is best known for an adaptation by one strain of E. Coli that allowed them to use citric acid as a carbon source.**

**3. Habitat/Niche:** **The primary habitat of E.coli is in the gastrointestinal tract (stomach and intestines) of humans and many warm blooded animals. The niche, or positions within a community of E.coli depends on the nutrient availability in the intestines of the host. A balanced ecosystem is maintained because there is a wide variety of these nutrient defined niches that are available in different parts of the intestines, creating an evenly dispersed population within the host. The preferred nutrients of different populations of E.coli will affect where these individual groups will reside. If E.coli is not able to adhere to the intestinal walls, then it will most likely migrate to the colon. E.coli can also be found in fecal-contaminated environments such as water and mud.**

**4. Predator avoidance:** **Flagella, which is a tail protruding from its exterior of its body, is used as a flipper to propel the microorganism away from predators. E.coli can fight for nutrients in areas of low concentration with a metabolic process called chemotaxis. Chemotaxis aids in the absorption of nutrients regardless of how scarce the nutrient levels are, and help E.coli bacterium avoid the death by starvation.**

**5. Nutrient acquisition:** **E.coli is a heterotrophic organism that gets nutrients from its host via biosynthesis, or combine organic molecules, of the nutrients that its host organism takes in. A three step central metabolic process is used to absorb excess glucose molecules in the intestines. Any excess salt molecules are also used for homeostasis. It also utilizes fermentation to convert pyruvate (essential molecule for cellular respiration) into ATP, allowing for high energy activity. E.coli utilizes a mechanism called solute transporters that absorbs nutritious molecules from the outside enviornment.**

**6. Reproduction/Life cycle:** **E.coli are single celled, asexual prokaryotes that reproduce via binary fission, a process in which the chromosomes are duplicated to create a genetically identical organism. The replication rate of an E.coli chromosome is approximately 1000 DNA base pairs per second. Conjugation, a sexual process, is used increases genetic diversity and spread beneficial adaptations within a population. In this process, genes from two individuals are transferred through sex pili or hairs ,that attract other E.coli organisms. Plasmids, or separate DNA molecules that are able to replicate,are used in conjugation to send signals out, and attract other bacterium to exchange genetic material.**

**http://www.nature.com/nrmicro/journal/v2/n8/fig_tab/nrmicro959_F1.html** media type="custom" key="24412364" align="center"

**Attached is a video of binary fission. I tried my best to embed it into the wiki; however, I am not sure how well that worked. (HB)**

**7. Growth and Development:** **The optimal rate of growth for E.coli is 37 C, but artificial strains can exist in temperatures up to 49 C. The growth is dependent on the nutrients available in the environment. If there are sufficient nutrients, then E.coli can grow at a constant rate until it is ready for mitosis( asexual cell replication). E.coli uses redox reactions to drive the anaerobic(without oxygen) and aerobic(with oxygen) processes of respiration ( the conversion of energy in nutrients in ATP, an energy filled molecule ) which stimulates growth of the cell. **

**8. Integument:** **E.coli's integument consists of a rod shaped cell wall. This wall applies in maintaining homeostasis(regulation of internal conditions), and transporting molecules in and out of the cell.The cell wall is made up of peptidoglycan, a cross link of carbohydrates and amino chains, and a phospholipid bilayer with membrane spanning proteins.These proteins along the membrane are used for transport of molecules in and out of the cell. The cell wall of E. Coli is two to three nanometers thick and composed of a few layers of peptidoglycan. An outer membrane of about seven nanometers thickness is also present in E. Coli; these membranes are composed of phospholipids (fats), lipoproteins(fat and protein), lipopolysaccharides(fat and proteins), and proteins. Porins or protein pores, facilitate the entry and exit of solutes through the cell wall.**

**9. Movement:** **E.coli swim around by either spinning thier flagellum(explained previously), or by literally tumbling through the cytoplasm.These extremities also help latch onto other surfaces of choice.** **E coli, similar to other bacteria, have been able to detect and direct themselves toward nourishment when starving, which is a process known as chemotaxis. As food around the E coli increases, a signal is transmitted to its flagellum motor which influences the movement of the bacteria toward the food. Two modes of transportation are counterclockwise rotation (or 'running' of the cell) and clockwise rotation (or 'tumbling' of the cell), with both being used to ensure proper nutrients are being provided to the E coli.**

**10.Sensing the Environment:** **E.coli can sense change in its surroundings' chemical composition, and can send electrical signals using multiple response systems to the rest of its body to respond. They can also tell if a particular area has a high or low concentration of nutrients to obtain the most nutrients possible. Surprisingly, It has been found that E.coli have a sense of touch. Physical/ chemical changes in the environment alter gene expression by changing the chemical/physical signals E.coli uses to sense the environmental changes.**

**11.Gas Exchange:** **Gas exchange occurs through its cell membrane.Simple diffusion by a difference in concentration gradients to diffuse gas across its membrane. Gas exchange also occurs through the process of anaerobic respiration.**

**12.Waste Removal:** **Active diffusion, the transport of molecules that requires energy, is used to secrete waste directly from the cytoplasm through the cell membrane.**

**13. Environmental Physiology:** **E.coli can survive in temperatures of 40-100 degrees Celsius, but 37 degrees Celsius is the optimal range. The desired pH level for E.coli is ~7(neutral). E.coli have certain measures for adapting to changing environments. Salt concentrations of up to 10% can be tolerated.**

**14. Internal circulation:** **As a single celled organism, E.coli has a very simple circulation system. Circulation occurs inside the cell when molecules In their circulation system, nutrients can be diffused into the membrane and waste products are diffused out. Nutrients are taken in and float through the cytoplasm until they arrive at where they need to be, or is picked/absorbed up by some small intracellular organelle.**

**15.Chemical control:** **E.coli does not have specialized cells or organs( groups of specialized cells working together for ex nerve cells make up brain) that control chemical exchange within the cell ; that would be impossible because E.coli is only one cell itself. Its chemical control is the the application of the cell wall's property, and the semipermeable** **membrane that regulates the molecules that enter and exit the cell. These molecules causes a reaction within the cell that causes change.**

**Review Questions:** **1.) How does E. Coli's circulatory system work? What type of system can this be characterized as?** **2) How do E. Coli achieve genetic diversity although they reproduce asexually?** **3) What unique property of E.Coli makes it helpful at nuclear waste sites?** **4) How is E.coli beneficial to humans and its hosts.** **5) How would an E.coli population react to an area where nutrients are scarce?**

**Sources:** **"Bacterial Asexual Reproduction (binary Fission) (English)." - Video. N.p., n.d. Web. 13 Nov. 2013. . - Binary Fission Video** **"Flagella and Philosophy." Zorknot. N.p., n.d. Web. 15 Nov. 2013** **[]** **http://medicalcenter.osu.edu/patientcare/healthcare_services/infectious_diseases/ecoli/Pages/index.aspx**
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 * http://www.cellsalive.com/animabug.htm **


 * http://www.cdc.gov/ecoli/general/index.html#what_shiga **