Monday, March 11, 2013
E. Coli
On pages 140 and 141 Dr. Sharon Moalem talks about Eschericia Coli or E. Coli and makes a connection to AP biology big ideas number 1 and number 4 (The process of evolution drives the diversity and unity of life and Biological systems interact, and these systems and their interactions posses complex properties).
How is E. Coli both needed yet extremely hurtful to the human body? Explain what a bad "strain" means. How is it possible for the lactose-intolerant E. Coli to lose its lactose intolerance (Explain using big idea number 1)? Define "Hypermutation" and how it pertains to bacteria and specifically E.coli. Also relate hypermutation to a different bacteria or organism other than E. Coli.
Posted by Madeline Merageas with email mmerage4@students.d125.org
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ReplyDeleteEschericia coli, more commonly known as E. coli, comes in many different variants or “flavors”. While most varieties of E. coli are harmless and result in relatively brief symptoms of infection (e.g. diarrhea), there are some particular nasty strains, which typically result in more severe symptoms of infection (e.g. severe abdominal cramps, bloody diarrhea, vomiting). These nastier strains of E. coli that have a greater impact on the well-being of the host are known as bad strains. For example, a common bad strain of E. coli is E. coli O157:H7, which results in the severe aforementioned symptoms above, and it typically takes longer for the host to fully recover when he/she is infected by a bad strain. While healthy adults usually recover from infection with E. coli O157:H7 within a week, young children and older adults can develop a life-threatening form of kidney failure called hemolytic uremic syndrome (HUS). Thus E. coli has earned a bad reputation because its bad strains have the potential to kill people if they gain access to the wrong part of the body.
Because E. coli has received such a bad reputation for causing severe infections because of its rare but present bad strains, it is easy to neglect the positive impact that the “good strains” of E. coli have on our bodies. E. coli is a digestive workhouse in humans and, in fact, “it’s one of the essential bacteria toiling away in [our] digestive [systems]” (140). E. coli boosts digestion through secreting digestive enzymes, which aid food breakdown. This enables energizing nutrients such as proteins to be absorbed fully and also prevents the accumulation of waste in the body. Also, the presence of E. coli stimulates an improved immune response. E. coli act like antigens, so it helps fight a variety of infections. Not only can E. coli behave like antigens and make the stomach more acidic by attaching to intestinal walls (and thus destroying any bacteria that make it all the way to the stomach), but it can also stimulate the production of antibodies, which provide defense against any infection.
Dr. Moalem states on page 140 that “nothing is a bigger threat [...] to bacteria than starvation”. Because starvation is an evolutionary pressure for bacteria, lactose-intolerant E. coli were forced to overcome this evolutionary pressure (and lose their lactose intolerance) in order to possess a selective advantage and be able to survive and reproduce. The bacteria’s ability to become lactose-tolerant was attributed to a massive increase in the mutation rate - regarding mutations that allowed the bacteria to lose their lactose intolerance - and this increased rate in mutations is known as “hypermutation”. Hypermutation involves many mutations along the bacterial genome, not just the ‘target mutation’ that is responsible for overcoming a specific evolutionary pressure. Somatic hypermutation (SHM) is a cellular mechanism by which the immune system adapts to the new foreign elements that confront it (e.g. microbes).
(Tina Moazezi - tmoazez4@students.d125.org)