In this lesson on aerobic and anaerobic bacteria, we’ll learn the characteristics of each and how they are similar and different. We’ll also give some examples of each type of bacteria.
Picture a world without oxygen. You might be imagining a barren wasteland like the moon, but in this scenario, the image is just the opposite. The environment is filled with hot volcanoes spewing life-giving chemicals into the aqueous world.
Somehow creatures co-exist with thousands of other species, all thriving in this unique ecosystem. What are these creatures? They are anaerobic bacteria. They are single-celled organisms that don’t need oxygen to survive, and in fact oxygen will kill them. They live in the hydrothermal vents of the deepest part of the oceans and use chemicals instead of sunlight to make food.Today, we’ll learn about anaerobic bacteria that do not need oxygen to survive, as well as their well-known counterparts, aerobes, which do need oxygen.
But first, what are bacteria?
Bacteria are small, single-celled organisms that don’t have a nucleus (a compartment to hold their DNA). They are called prokaryotes. Other more complex cells, like the ones in our bodies, are called eukaryotic.Bacteria can be anaerobic or aerobic. Aerobic means involving oxygen, so anaerobic bacteria can survive without oxygen.
Normally, organisms use oxygen to make energy, but these organisms have found ways to get around this. All organisms make energy through cellular respiration, but they do this differently depending on if they are anaerobic or aerobic. In this lesson we’ll look at the different types of cellular respiration and then show some examples of each type of bacteria.
Cellular Respiration Types
Before we get started, let’s go over some basics about cellular respiration. During cellular respiration, cells use a series of chemical reactions called oxidation-reduction reactions to move electrons around.
Cells take electrons from sugar, or glucose, and use the energy stored in them to make ATP, or the energy currency of the cell. Think of cellular respiration as a factory where raw materials like glucose come in, are made into products, and then sold to make money or ATP.
All anaerobic bacteria make energy without oxygen. They do this in one of two ways, either through lactic acid or alcoholic fermentation. During lactic acid fermentation, cells use a molecule called NADH to take electrons from glucose. The NADH use the energy stored in the electrons to make ATP, and convert glucose to pyruvate. This process is called glycolysis and is the first step in all forms of cellular respiration.
In lactic acid fermentation, the next step is to pyruvate to lactic acid. Lactic acid, although a waste product for bacteria, can be used to make human foods, like yogurt.The other way anaerobes make energy is through alcoholic or ethanol fermentation. Like in lactic acid fermentation, NADH takes electrons from glucose and turns it into pyruvate during glycolysis. From here, the pyruvate is converted to ethanol instead of lactic acid. This is the same ethanol that we find in beverages like wine and beer.
Alcoholic fermentation also makes carbon dioxide, which gives beer the carbonation.
Aerobic bacteria are much more efficient at making energy. Anaerobes only make two ATP molecules per glucose, but aerobes can make up to 38 ATP per glucose. Aerobic respiration can be broken down into three steps: glycolysis, the citric acid cycle, and oxidative phosphorylation.Glycolysis occurs in the same way as anaerobic bacteria.
Glucose is converted to pyruvate and NADH collects electrons. But instead of stopping there, aerobes take the pyruvate and shuttle it to another step called the citric acid cycle. Here, more NADH and some ATP is made from pyruvate in a series of chemical reactions and carbon dioxide is made as waste. After that, all the NADH head to the mitochondria, or powerhouse of aerobic cells. There, the cell works hard to harvest lots of energy from the electrons stored in NADH using oxygen.
Helpful Anaerobes and Aerobes
Although we typically think of bacteria as causing infections, both aerobes and anaerobes are helpful to us. The anaerobe lactobacillus bulgarius does lactic acid fermentation, which provides the tangy flavor and nutritional benefits we get from yogurt.
Bacteria can also be helpful to plants. The aerobic soil bacteria rhizobium lives in symbiosis with plant roots. The bacteria convert nitrogen to a form that plants need to grow and, in turn, get a home from the plants.
Harmful Anaerobes and Aerobes
If you ever see a can with an expanded lid after being sealed, beware! This may contain the dangerous anaerobe clostridium botulinum which causes botulism poisoning.
It uses ethanol fermentation to make energy and can be found in soil and occasionally in canned foods. The bacteria produces a toxin called botulism that can cause paralysis and death if consumed.Aerobic bacteria aren’t always our best friends either. Mycobacterium tuberculosis is the causative agent of tuberculosis, a highly infective disease of the lungs. This aerobic bacterium has very thick cell walls, making it hard for the body to destroy.
It infects the lungs of patients, causing a thick cough with bloody mucus.
In summary, bacteria are single celled microbes without a nucleus. Anaerobic bacteria make ATP without oxygen. They either do lactic acid fermentation, where glucose is used to make lactic acid and two ATP, or ethanol fermentation which also uses glucose but makes carbon dioxide, ethanol, and two ATP.
Aerobic bacteria use oxygen and glucose to make 36-38 ATP and carbon dioxide. They do these through three steps, glycolysis, the citric acid cycle, and oxidative phosphorylation, where oxygen is used.
|*3 steps: glycolysis, citric acid cycle, oxidative phosphorylation *Oxygen and glucose are used to create 36-38 ATP and carbon dioxide||*Lactic acid fermentation: glucose is used to make lactic acid and 2 ATP *Ethanol fermentation: glucose is used to make carbon dioxide, ethanol, and 2 ATP|
When you are done, you should be able to:
- State some of the characteristics of bacteria
- Explain how bacteria create energy
- Compare the respiration processes of aerobic and anaerobic bacteria