Part 2

Where in the world? Where can you find bacteria? The short answer is… everywhere! Wherever you look, you'll find them doing amazing things. Here are just a few places you can go hunting for bacteria. Ocean Bacteria are found at all depths of the ocean. At the surface, they take in energy from the sun. On the ocean floor, they get energy from chemicals. Air and sky There are bacteria floating in the air around you, as well as in the atmosphere up above your head. Some bacteria even live inside clouds! Rocks Some bacteria can survive inside rocks. There isn't much there to eat, so they grow slowly and reproduce only every 100 years or so. Soil Soil is jam-packed with bacteria. The bacteria that live in soil can turn nitrogen in the air into useful nutrients for plants. This is part of a process called the nitrogen cycle. Nitrogen cycle Nitrogen is a gas that's in the air, in a form plants can't use. Bacteria in the soil turn nitrogen into fertilizer. Plants use the fertilizer to grow. Animals eat plants. Animals pee, poop, and die, and plants die, too. Decomposers, such as worms and fungi, break down the pee, poop, and dead matter back into fertilizer. Other kinds of bacteria can change fertilizer back into nitrogen. At home Your home is full of bacteria, but don't worry—most of them are completely harmless. You might find some dangerous ones on surfaces that aren't properly cleaned. In you! Bacteria play a big role in your body and on your skin. In fact, there are more bacteria cells in your body than human cells! A person carries about 4.4 lb (2 kg) of bacteria in and on their body.

Can a squid glow? The bobtail squid is an amazing animal. It lives in the shallow waters of the Pacific and Indian oceans. At first glance, it appears to be glowing! Can you guess what is really making it shine? Look inside Bobtail squid have special bacteria living in them. Chemicals inside the bacteria make them light up. This is called bioluminescence. Bacteria help the squid hide from animals below by matching the brightness of the waters above. Bobtail squid grow to about 1.2 in (30 mm) long. That's seven times smaller than the average squid. LIGHT IT UP Bobtail squid aren't the only living creatures that glow in the dark. Check out these other super shiners. Mushrooms When fungi like mushrooms make light, we call it fox fire. They use their green glow to ward off hungry predators. Anglerfish Female anglerfish have a body part full of glowing bacteria on their heads. It helps them lure in prey and find mates. Plankton These waves crashing on to a beach in the Maldives, South Asia, are full of tiny bioluminescent plankton. The light confuses their predators.

In your body Humans are born without bacteria, but our bodies are quickly inhabited by hundreds of species. Although we often think of bacteria as evil critters that make us sick, most are harmless— and some are even helpful. What's that smell? Most of the bacteria in your body can be found in your gut, where they help you to digest, or break down, your food. But they also have an embarrassing side effect—one you may notice if you eat too many beans… 1 Mouth The first step is chewing! Food must be broken down into smaller parts before it can be used by your body. Muscles in your throat push the food into your stomach. 2 Stomach Food is broken down further by acid in your stomach. The resulting goop is then passed to your small intestine. 3 Small intestine Special snippers called enzymes cut up long food molecules that your body can't use into shorter ones that it can. But the enzymes don't work on big molecules called oligosaccharides found in some foods, such as beans. 4 Large intestine The oligosaccharides pass to your large intestine. Bacteria there can break them down. As they do, the bacteria produce hydrogen and methane gas, which builds up until you fart it out.

The bad guys Most bacteria are harmless. Some are even helpful. But some can cause us to feel unwell. These harmful bacteria have clever ways of getting from one human host to the next. Cholera Cholera is a terrible illness that spreads easily in places where the drinking water is not clean. In 1855, scientist John Snow discovered that a cholera outbreak in London, England, was caused by something in the water. 1 Bacteria multiply Cholera bacteria multiply inside the warm, moist digestive system of its victim. They attach themselves to the lining of the small intestine and release dangerous chemicals called toxins. 2 Diarrhea The toxins cause the person's body to pump water into the small intestine, making their poop very runny. About half the weight of your poop is bacteria. 3 Cesspool In the 1800s in London, the toilets emptied into underground cesspools. Watery diarrhea helped the cholera bacteria flow easily through any cracks in the cesspool wall. 4 Infected water supply Cholera bacteria seeped through cracks into an underground well. Before people had tap water, they would pump water from wells for drinking. 5 Contaminated water When people drank well water contaminated with cholera bacteria, they became infected. Once John Snow realized what was making people ill, the water pump was shut off. 6 Symptoms pass on This new victim now has diarrhea, too! She will add more cholera bacteria to the cesspool. 7 Cycle continues Cholera infected more drinking water and spread the disease to new victims. Whooping cough Whooping cough bacteria causes a sticky substance called mucus to build up in the lungs. The victim must cough to clear it. This sprays bacteria into the air, and other people breathe it in. Acne Acne bacteria live harmlessly inside little holes in your skin called follicles. When a follicle gets blocked, the bacteria feed on oils that build up, and multiply. Your body fights back with red swelling called inflammation—a pimple!

Your body's defenses Your body has all sorts of ways to defend itself against harmful microbes, or germs. Together, these defenses make up your immune system. Your immune system's first line of defense is your skin. Cut Your skin is your biggest organ. It's a tough layer of armor around your body. When it's cut, the tissue underneath is exposed to germs, which can cause infection. The blood in your body flows through a system of tubes called arteries. Inside your blood are different types of white blood cells, all with different ways of fighting germs. Dangerous bacteria and germs can't get through your skin. When you get a cut, your immune system sends more bacteria-fighting blood to the area, causing your skin to become red and swollen. Bacteria can produce toxins that hurt your body. This type of white blood cell releases chemicals to fight those toxins. This kind of white blood cell releases chemicals called antibodies that kill or stun invading germs. Then the macrophages can easily gobble them up. ALLERGIES When your immune system attacks something that isn't harmful, such as pollen, it's called an allergy. Having an allergy to pollen is called hay fever. OTHER DEFENSES Your immune system has a few other tricks that help to stop an infection in its tracks. Fever When you have a fever, your body temperature is higher than normal. Fevers fight germs and help white blood cells work better. Sneezing Microbes in your nose can make you sneeze. Sneezing helps to expel the germs, keeping you healthy. Tears Germs can irritate your eyes. The tears they cause try to flush them out.

The story of antibiotics There are ways to avoid getting infected by bacteria, such as washing your hands and not touching your eyes and mouth. If you already have an infection, however, your doctor might give you medicine. Medicines that fight bacteria are called antibiotics. Amazing discovery There used to be no treatment for deadly bacterial infections such as pneumonia. Then, bacteriologist Alexander Fleming accidentally discovered something amazing. In 1928, before leaving for a trip, Alexander Fleming set up bacteria samples to grow in petri dishes while he was away. When he returned, one sample looked very strange… Fleming had left his lab a little messy. Different substances had gotten into the petri dishes. One of them had some mold in it. Mold is a type of fungus, and it had a surprising effect on the bacteria. Fleming figured out what had happened. The hungry mold, called penicillium, had killed nearby bacteria competing for nutrients by releasing a molecule we now call penicillin. The penicillin had made the bacteria cells pop. Over time, scientists figured out how to separate the penicillin from its mold. Penicillin is now used to treat bacteria infections all over the world. But then... BACTERIA FIGHT BACK! Bacteria don't give up easily. They can get used to an antibiotic, causing it to stop working. This is why scientists are always on the hunt for new antibiotics. Antibiotic mostly works An antibiotic can kill bacteria, but some cells that are slightly different, or mutated, survive. Antibiotic stops working The mutated bacteria grow and multiply. The old antibiotic doesn't work too well on these bacteria. New antibiotic works New antibiotics are found that kill the mutated bacteria. But new mutations continue to form...