All living things need a way to get energy. Bacteria get their food and energy in many ways. Some bacteria can make food on their own, while others need other organisms.

Some bacteria help other living things as they get energy, others hurt them while they get energy, and still others have no affect on living things at all.
Some living things, or organisms, are able to make their own food in a process called photosynthesis.

In this process, the organism turns energy from the sun into energy that can be used for energy. Organisms that get their energy from photosynthesis are called autotrophs. Some bacteria get their energy this way.

Some bacteria, called chemotrophs, get their energy by breaking down chemical compounds in the environment, including ammonia. Breaking down ammonia is important because ammonia contains the element nitrogen.

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All organisms need nitrogen to survive, and the nitrogen released by bacteria is crucial to these living things’ survival. Clearly, chemotrophs are very important and beneficial to other living things. Living things that cannot get their energy through photosynthesis or from breaking down chemical compounds have to get their energy from other living things. Some bacteria, called decomposers, get their energy by breaking down dead organisms or waste products into simple nutrients and energy.

Pseudomonas bacteria are decomposers found in the soil, where they recycle dead plant material. The last groups of bacteria get energy from organisms that are still alive, and depend on these organisms to survive.
Mutualistic bacteria get their energy in ways that help another organism. For example, some bacteria live in the roots of legumes, including pea plants. The bacteria make the nitrogen the pea plants need and the pea plants provide a place for the bacteria to live. Other bacteria, called parasitic bacteria, hurt the organism they are getting help from. For example, some bacteria cause illness. We will talk about ways bacteria can be helpful or harmful a little later.

All living things reproduce. This is the only way to ensure the organisms continued survival. Bacteria reproduce asexually. This means that a single “parent” organism produces offspring on their own. In the case of bacteria, a process called binary fission is used. In binary fission, the DNA in the nuceleoid region and plasmids double, and the bacterium splits into two identical copies. If everything happens the way it’s supposed to, the two new bacteria will be identical to the original bacterium. These bacteria can then split again to increase the number of bacteria in the population. Through binary fission, bacteria reproduce very quickly. Some populations can double their size in less than ten minutes!

How to Grow Your Own Bacteria

Although we often think of bacteria as things that cause disease, some bacteria are very helpful. In fact, if you like to eat yogurt, you are eating helpful bacteria all the time! See for yourself in these two activities:

Materials:

• clean plastic cup
• yogurt
• dropper or toothpick
• microscope with slides and coverslips

1. Place a very small portion of plain yogurt onto the slide, and add one drop of water. Place the coverslip on top.
2. Under low power, find a section where the yogurt is pretty thin; this is where you will find the bacteria.
3. Switch to high power (400X for most microscopes) for a better view of the bacteria.
4.  Make a sketch of your view under different magnifications.

Finding Bacteria in Yogurt

Materials:

• clean plastic cup
• yogurt
• toothpick
• water
• microscope with slides and coverslips

1. Clean a small plastic cup. Make sure ALL soap is completely rinsed off.
2. Put a small amount of yogurt in the cup, and put it aside in a dark, relatively warm area. Leave undisturbed for at least 24 hours.
3. After the time has past, take a small sample with a toothpick and place on a slide. If the sample seems too thick, dilute with a drop of water. Next, place a cover slip on top.
4. First observe the bacteria at low power 100X to find a good place to start looking. The diaphragm setting should be very low (small) because these bacteria are nearly transparent.
5. Switch into the highest power to identify the bacteria according to arrangement.
6. From here you can identify any bacteria you might find. For example, a common inhabitant of yogurt is a paired, round bacteria or diplococcus (see list below)
7. Did you observe more bacteria in part 1 or 2? Why do you think this is?
8. Do you want to take it a step further? Think about all the kinds of yogurt out there. There are different flavors, different brands, some that are non-fat, and much more. Do some types have more bacteria than others? This is a great question to investigate using the scientific method. So come up with a specific question, write a hypothesis, grab some yogurt, and get experimenting!

Bacteria are classified as follows:

First observe the way the bacteria are arranged:

• paired = diploe
• chained = streptose
• clusters = staphyle

Next observe the shape of the bacteria:

• round = coccus
• rod = bacillus
• spiral = spirillum

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