Content Objectives
The topic of microbes ruling the school is sure to be an exciting and relevant topic for middle school. After all, these particular students are smelly, goofy, and excitable. They are not focused on anything but themselves and each other. So, I need to get these students' attention. When I can make a connection to their everyday lives, they get engaged. After several years of teaching, it seems that the nastiest and most gross topics get middle school students' attention. Not that microbes are gross (after all, they're microscopic), but infectious diseases that are caused by microbes are mucho gross to adolescents. Sex, fecal matter, poison mushrooms, trash, sickness and diseases, and gross images are sure to engage middle school students. Violence, drama, raunchy hip-hop music, cell phones, sports figures, and celebrity drama are often discussed in class. The students' developing bodies are often an engaging topic in class. Prestigious athletic shoes are also prized in school. Students often take their shoes off and smell them, as well as each other's shoes, while they are checking them out! What's up with that? Video games are often played in class, whether teachers like it or not. I really could get students engaged if I could relate science to all these student conversations. How about a video game about viruses or the many different types of bacteria? How about a killer virus that preys upon unsuspecting bacteria? Some viruses called bacteriophages land on a bacteria cell like a lunar lander, implant DNA into the cell, and replicate viruses like a copy machine, until the cell explodes. These are very violent scenarios that are happening in the human body right now in real time. Or how about a cell phone app on infectious disease that could be applied as a group activity in the classroom? Perhaps an activity about why fungi and bacteria cause odors in sneakers? Well, guess what? Microbes are not all bad, in fact we must have them around to live. These topics and concepts are what I am going to present in this unit. I will demonstrate in this unit, how humans need most of these microbes to live and how they affect every biotic and abiotic thing on the planet.
Microbes are an effective topic for the engagement of middle school students, because in the microbial world, you have destruction, violence, sex, history, ecology, evolution, global warming scenarios, and video game action. I have created a curriculum unit to exploit all this drama that happens in the microbial world. The human microbiome is an emerging science with limitless possibilities for mankind. Microbes are related to almost every topic in my 8th grade integrated science class. In this Curriculum Unit (CU), I intend to show to middle school educators accessing this material, the importance of microbes in the world, and how they can be used to engage middle school students. As I stress throughout this unit, microbes can be related to most any area of a science middle school curriculum. Along with the activities, I stress common core standards of reading and writing for science topics and describe the activities and concepts learned in and out of class. Also equally important, is the discussion of content knowledge. I will give some interesting facts and background stories you won't find in a textbook.
Background
The school in which I teach is a high needs, low performing middle school in a large inner city metro area. The students struggle with any learning outside of their cell phones and iPads. They have no relationship with the outdoors and the physical world around them. They don't know how much money their parents pay for utilities. They have no idea what it takes to be healthy, the kinds of microbes are on or in their bodies, and very little about infectious diseases. They think the ocean is a distant place that has no relationship with the places they live.
This CU addresses 8 th grade integrated science at a middle school in Charlotte, North Carolina. With 1200 or so students, the school is located in an affluent area of Charlotte, located near The University of North Carolina at Charlotte in the prestigious Research Park area of North Charlotte. The demographic makeup is approximately 90% African-American and the rest mostly Hispanic students. 80% of the student population receive free or reduced lunches. Charlotte and this school system see a large transient population, with some students living in hotels. Most students (60 %+) read below grade level and are seldom seen reading books. These students own tablets and smart phones, however, reading comprehension is weak in all subject areas. Reading and writing effectively about observations, science activities, and experiments are difficult for them.
This situation requires scaffolding and differentiation strategies while staying true to the Common Core Standards and New Science Essential Standards that are required for students to pass the North Carolina 8 th grade science End of Grade Test and transition into high school. North Carolina End of Grade Tests are packed with higher order questions, not just memorization questions, and for this reason it is imperative that students effectively analyze, write, and describe concepts and demonstrations performed and discussed in the classroom.
Microbes and Curricula
I want to let the teacher-reader know that this CU is not written as a textbook, but as an addition to previous knowledge that a teacher might have learned while attending college or professional development seminars while teaching. I attempt to keep the writing informal and discuss recent advances in microbiology, pedagogy, probiotics, and how microbes affect our everyday lives. After all, we teachers know how to get a student's attention by relating the content to their everyday lives. One topic to exploit is odor of the sneakers worn by students at school. Middle school students are fascinated with sneakers and who has which brand of sneakers. The cost is as important as the smell. How many times have you witnessed students passing their sneakers around to smell and adore them? Because their lives revolve around their shoes, we have a perfect opportunity to create a lesson on odor causing feet fungi and bacteria! Infectious disease can also be connected to middle school life, because many students have had an infectious disease or know someone who has. Infectious diseases are a fascinating subject for students to make a connection with, and thus helps engage them in class.
Microbes affect every part of our life and environment. The human microbiome is a complex microcosm that lives in and on the human body. Most of the microbes in our biome are necessary for our survival and have a beneficial relationship to us. They indeed rule our schools, bodies, global and local climate, and ecosystems. For example, schools have many microbes lurking in them ready to be sucked up someone's nose or drift into a student's ear. Most are beneficial to humans and we don't need to go around randomly killing microbes. That's where we get into trouble with antibiotics resistance, because bacteria tends to build up resistance to antibiotics over time. Some autoimmune diseases, such as peanut allergies may be caused by human attempts to manipulate our living environments and make us cleaner, which then alters the species in our microbiome and confuses the immune system into attacking the body by mistake. Most bacteria are beneficial, and humans tend to focus on the infectious disease microbes, without paying attention to all the so-called good microbes that we attempt to kill with anti-bacterial soap and dish detergent. Some scientific studies suggest that we shouldn't use anti-bacterial soap at all. We use anti-bacterial products thinking we will rid the world of microbes, however, we will never be able to rid the world of bacteria and viruses, and we really don't want to kill the beneficial microbes. Because they are so are so numerous and can live in extreme conditions for long periods of time, the effort to rid our bodies and environments from them is futile.
These bacteria, viruses, and fungi can survive and thrive in frozen conditions, and in extreme acidic and toxic locations, such as volcanos and under the ocean near hydrothermal vents, without light or photosynthesis. These bacteria and microbes that can withstand extreme conditions are called extremophiles. Deep in the ocean, where no light can penetrate, some types of bacteria use chemosynthesis instead of photosynthesis to create their own energy. These bacteria species called extremophiles are very interesting and very engaging to students and this subject can be exploited with some planning and creative activities.
Viruses: Friend and Foe
Viruses, the smallest of our microbial friends, live secretly in places we would never assume. They also perform activities and functions that science fiction writers use to make millions of dollars and impress their readers and movie-goers with their creativity, when in fact, they just get their ideas from the viruses themselves. Viruses are my favorite microbe because they are considered non-living and don't have cells. Just because they are non-cellular doesn't prevent them from doing amazing things for all life on the planet, as well as causing havoc in human beings at times. We cannot live without them. Albeit, some are strange looking, as they might have arrived here from another planet. Bacteriophages, the types of viruses that attack bacteria, sometimes look similar to the lunar lander created during NASA's Apollo era. All viruses do have genetic material and do some amazing things. They don't reproduce on their own, instead they replicate like a copy machine, using a host cell's energy to make more viruses. And viruses live everywhere; inside our bodies, in toxic environments, deep under the ocean, and even in unlikely places such as under thick layers of Antarctic ice. Cyanobacteria use their photosynthesis genes to make roughly 50% of the oxygen we breathe while their viruses, called cyanophages, also have these genes, and help create about 5% of the oxygen we breathe. Also, genes from viruses comprise about 8% of our human genome. Now, some scientists are saying that all life on earth could have evolved from viruses.
How can a living organism evolve from a so-called non-living virus? I prefer the term non-cellular myself, because the viruses do contain protein and genetic materials, similar to cellular life. Whether viruses are alive or not, is a very controversial issue because they lack cells and cell processes. The genetic material contained inside a virus depends upon the category and type of virus family to which it belongs. Virology is a growing field in science, as scientists are still discovering them faster than one can catalog them.
When Lita Proctor was a graduate student at the State University of New York at Stoney Brook, she decided to research how many viruses (if any) were in seawater. Proctor estimated there are at least 100 billion viruses in every liter of sea water. 1 So, the volume of a two liter soft drink bottle would contain a huge number of viruses that help contribute to the survival of the human race and all life on the planet, through oxygen made by their photosynthesis genes. Of course, we know that viruses are so much smaller than bacteria and many viruses can live inside a one-celled bacterial host. Ocean dwelling viruses are so powerful that they infect a new microbe host ten trillion times a second and kill about half of all the bacteria in the ocean every day. 2
So what role do viruses play in creating oxygen for us to breathe? As I stated earlier, viruses play a part in creating about 5% of all the oxygen in the world. The viruses that live in the ocean contribute to the manufacture of all this oxygen. An abundant species of ocean bacteria, called Synechococcus, carries out about a quarter of the world's photosynthesis. 3 Scientists examined theses bacteria and found virus genes carrying out their light harvesting. And researchers have found free-floating viruses carrying the photosynthesis gene searching for a new host bacterium to infect. A rough calculation showed 10% of all photosynthesis on earth is carried out with a virus gene. 4
Viruses contribute to the success of all life on earth. However, they are also killers. Viruses such as the HIV virus can mutate very fast; that's the reason why HIV easily mutates to resist drugs and remains so deadly. Of course we know HIV causes AIDS. Doctors and scientists have developed a cocktail of different drugs and treatments to combat HIV. These drug cocktails confuse the viruses and this helps slow progression to AIDS (destruction of the immune system allowing any pathogen to enter the body and cause disease), because even HIV cannot mutate fast enough to overcome the complex mixture of drugs Although, only a very small percentage of viruses cause illness or death in humans, we are very aware of the ones that do. For example, the disease Smallpox, which is caused by variola virus, has been is said to have killed more people than any other disease in history. We don't have to worry about smallpox anymore because it has been eradicated through a global campaign to vaccinate people against the virus. Modern medicine has successfully eliminated this one killer virus of humans, but is it gone forever? Controversially, stocks of variola virus still exist in labs in Atlanta at the CDC and in a lab in Siberia. Smallpox caused epidemics and pandemics, killed people throughout the ages, and a lab accident or bioterrorism could cause the virus to kill again.
Common cold viruses, although not deadly, cause annoying symptoms that make us dread them like the plague. Human cold viruses, especially rhinoviruses, is one of the most prevalent viral diseases in humans. Why can't we prevent or cure the common cold? One reason we can't cure the common cold is that our many antibiotics are ineffective on viruses and instead, only target bacteria. Also, rhinoviruses cannot be controlled by a vaccine because these viruses mutate so fast; constantly changing and evolving in just a short amount of time. By the time a vaccine is developed for a certain strain, it would have already mutated into a different type. All life on the planet must rely on viruses to survive and all life can be sickened or killed by viruses as well.
The Good and the Bad Bacteria
In my opinion, the lowly bacteria, single celled, and always microscopic, don't have the hip-hop star quality and fascination to science that viruses do. Bacteria are critters that can be defeated with antibiotics (or at least this used to be true before many of them evolved resistance). Scientists also debate which microbe evolved first, the virus or the bacteria. In my opinion, I would like to think viruses were here first, and came from outer space on a rogue asteroid from some strange world. I have no proof of this of course. There have been several books written on the subject, as well as TV shows. Bacteria can make us sick, or even kill us. When I think of bacteria, I think of strep throat. The bacterium streptococcus, which causes strep throat, is identified by doctors by simply swabbing the throat and peering through a microscope. At that point, an antibiotic is prescribed if it is a bacterial infection, but not prescribed if it is a viral infection.
Scientists at the Massachusetts Institute of Technology have discovered evidence concerning a mass extinction that occurred 252 million years ago. This mass extinction was one of the greatest in the earth's history. This event is commonly called The Great Dying. According to their article, large amounts of gene transfer (AKA microbe sex) occurred to create huge amounts of methane gas released into the atmosphere. 5 This release of methane gas changed the makeup of the atmosphere and caused climate change and global warming, thus resulting in the largest die-off of life in the earth's history. You won't find any fossil evidence of bacteria and viruses, however, they is plenty of evidence they have affected all life on the planet throughout history (that is another curriculum unit).
Bacteria are with us from day one, coating our tiny bodies in bacteria-laden vaginal secretions as soon we exit the womb. 6 At the first minutes of birth, the baby becomes a microbe-symbiosis mammal containing 100 trillion bacteria. The newborn is also exposed to fecal matter containing bacteria. All this bacteria is introduced into the body and gut by swallowing, and to the nose by breathing, and of course when a stranger holds the baby other foreign bacteria are transferred into and onto the previously sterile baby. After a few days things settle down and the bacteria start to help the baby be healthy by aiding in the digestion of the mother's milk. So, we are thrown into the world of microbes in the first few seconds of life. Eventually, the cells in the human body are outnumbered 10:1 by microbes performing various duties for us in the gut and on our skin—some good and some not so good. Hopefully, this balanced symbiotic relationship continues to be beneficial to both the host and the microbes, keeping the healthy human biome healthy.
The Relationship between Viruses and Bacteria
We can think of viruses that attack bacteria as having a predator-prey relationship. Viruses are so very different from bacteria because they are considered non-living or non-cellular. Viruses can only reproduce when they attach themselves to a cell and implant their genetic material into it. At that point, the virus replicates inside the cell and eventually the virus reaches the maximum amount of proteins for new viruses to be assembled inside the cell. When the cell cannot hold all the new viruses, the cell rips open and release an entire new batch of viruses ready to go out and infect other cells. The virus destroys its host cell, period. But in many cases, as is happening in seawater at this moment of time, the virus actually assists the photosynthesis process by providing a helping hand to the cell. Some viruses have the gene which contains the photosynthetic material which actually helps the bacteria be more productive in the production of oxygen during photosynthesis. Usually, the virus hunts down and eventually destroys the bacteria cell by replicating inside. In the case of viruses in the seawater, the virus implants DNA into the bacteria which assists the cell and then kills it through a rapid voracious copy machine like process, which results in the eventual explosion of the cell. Viruses kill about half of the bacteria in the earth's oceans every day. Proof of this is the white cliffs of Dover which contain millions of years of layers of dead microorganisms, where viruses were a major source of the mortality. Viruses are deadly, but can be used in medicine to kill harmful bacteria that make us sick, by providing an alternative therapy rather than traditional chemical antibiotics. Such therapies are examples of how humans can benefit from this type of symbolic relationship between bacteria and their viruses.
Probiotics and Food and Energy
Research also has shown that there is a symbiotic relationship between the human body and the microbiome. Research shows this relationship can become unbalanced and cause problems for the human body associated with various diseases such as obesity, Crohn's disease, autoimmunity diseases and others. This community of dietary microbes in our gut is called enterotypes. Adding food from a low-fat diet, high fiber diet in the long term can change the types of microbes in the gut, especially the proportion of bacteroidetes present. 7 Recent research has shown the importance of a healthy and balanced microbiome. The practice of introducing probiotic bacteria to reach a balance and assist in the regulation and digestion of food energy has shown some promise in balancing the microbiome. Probiotics are living organisms that are used to change or add to our gut microbiome to improve the balance of beneficial microbes in our bodies to improve our health and possibly help ease the symptoms of some chronic diseases. Many companies promote their products as helpful in maintaining the correct balance of bacteria in the gut.
There is even a website for a company that will analyze your microbiome sample and give suggestions on how to balance the bacteria in your gut. But this is controversial, because scientists are still discovering which bacteria should and should not be present in the gut. According to recent studies, the types of bacteria in your stomach will correlate with your weight. The ratio of two genera of bacteria, Prevotella and Bacteroides, parallels the amount of plant carbs in your diet. In western countries, diets high in animal protein and saturated fats reflect more Bacteroides bacteria, and different diets for people living in certain areas of Africa show more Prevotella bacteria. 8 If you want to lose weight, apparently you should adopt a diet which encourages a Prevotella enterotype. According to recent studies, the proper types of bacteria and the right balance of bacteria in the gut can result in weight loss, and better health in general.
Seawater: Interactions of Bacteria and Viruses that affect the Climate
Ocean water contains many different substances. Among them are dissolved oxygen, minerals, salt, microscopic life, such as algae, and surprisingly, bacteria and viruses. There are an estimated 100 billion viruses for every liter of seawater. Through processes and reactions that occur in the oceans, microbes control the makeup of our climate. There is a surprising interaction involving oxygen, bacteria, viruses, and ocean water that affects every living thing on the planet and the climate. With that being said, why and how do viruses and bacteria interact to affect the climate? Not only do viruses control the amount of oxygen created in the ocean and on the earth, but directly affect the ecology of the oceans and earth's global climate. 9 Emerging research may or may not show that human activity through the accelerated release of greenhouse gases has perhaps affected the delicate microbial balance in the ocean. If you have ever researched global warming, you know that the amount of carbon dioxide, methane, oxygen, moisture and dust in the atmosphere dictates the amount of sunlight that reach plants and animals on earth. As I mentioned before, viruses kill about half of all bacteria in the ocean every day and algae and photosynthetic bacteria create about 50% of all the oxygen we breathe. Some microbes absorb and release large amounts of carbon dioxide into the atmosphere. Releasing too much carbon dioxide into the atmosphere would allow more global warming through the greenhouse effect. Algae and photosynthetic bacteria absorb carbon dioxide and make the planet cooler (think about the reaction that occurs during photosynthesis but on a global scale). When microbes in the ocean die, they absorb carbon, which cools the planet. These marine microbes occur in huge numbers and make up most of the biomass on earth. Marine snow (the fall of dead organisms to the bottom of the ocean) absorbs huge amounts of carbon. This is one reason scientists think of the ocean as a huge carbon sink or sponge, and again, too much carbon dioxide equals more global warming. So as I have said though out this CU, viruses rule and a delicate balance is present in the oceans.
Chemical and physical reactions occur amid habitats in photic and aphotic zones. Microbes are fundamental in ocean floor sediment formation and there is life under the seabed. Biofilms are dense sheets of bacteria created on surfaces of objects and living organisms. Modern scientific methods and advances in technology have led to new ideas and discoveries about the evolution of microbial life. Ocean research is suggesting that human activity through the accelerated release of greenhouse gases has affected the delicate microbial balance in the ocean thus far. The increased acidity of the ocean affects microbes as well as all life in the oceans. Also, remember that photosynthetic microbes can only live in the photic zone of the ocean where sunlight can penetrate to complete photosynthesis. Microbes rule the oceans as well as land areas.
Fungi, Sneakers, and Feet
In order to connect the sometimes bad smell of sneakers in school to bacteria and fungus, we need to know why this smell occurs. Sometimes it might be the feet, socks, or actual sneaker itself. Let's discuss which fungi or bacteria are the masterminds of all this odor. At any given time, millions of bacteria live on our feet, along with fungi, molds, ammonia, and denatured proteins. Like all living things, these organisms on our feet have survival activities which consist of food intake and the production of waste. Bacteria will consume dead skin cells and naturally, produce waste. It is the waste material that is often the cause of shoe odor. As physical activity increases, bacterial growth, waste and odor intensify. The primary culprit is sweat. The human foot has around 250,000 sweat glands that produce around 1 cup of perspiration per day. Interestingly enough, sweat itself has no odor. It is sweat in conjunction with other factors that can lead to having stinky feet.
There are several types of bacteria associated with causing foot odor. The most common is Brevibacterium. Found primarily on feet, it eats and survives on dead skin. As it eats, a gas known as methanethiol is produced. It has a sulfur like aroma that has been compared to that of cheese or rotting cabbage. Amazingly enough, Brevibacterium is used in the fermentation processes of certain cheeses. Propionibacterium is a rod shaped bacterium found mostly in the sweat glands. It has the ability to metabolize amino acids contained in sweat into propionic acid. Propionic acid is commonly found in sweat and is recognized by a strong, vinegar smell. Staphylococcus epidermis is a bacteria not only found on feet, but all over the human body, as well. As it interacts with sweat, it produces isomeric acid which is known to have a cheese or musty odor. It is amazing how many chemical reactions and processes that go into the smell of dirty feet.
Fungi are other major players that live around the toenails and on feet. Actually, there are about 100 different species of fungi on our feet. 10 A team of scientists studied the locations of microbes on the human body and found the greatest concentration of microbes were on our heels. 11 Our feet are attractive to certain colder-loving fungi because the extremities are a little cooler than our core body. Julie Segre, senior investigator at the National Human Genome Institute, states that fungi also offer important benefits to our skin as they help keep disease causing bacteria from sticking to our skin. She also says that attempting to rid our skin of these beneficial microbes is not the best decision. 12 It is amazing that there are huge numbers of species of bacteria and fungi, just on our feet. This reinforces the notion that microbes rule our schools, our bodies, and the entire planet. One could write a book or teach an entire year on the reactions chemicals, and microbes that are involved in the smell of dirty feet and sneakers. Science teachers realize that everything is very complicated in the world of science, and microbes are no exception.
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