How long does bacteria exist in agar?

When you mix agar and bacteria in a petri dish bacteria forms. How long does the bacteria last? After you leave the bacteria in the dish overnight, you are able to see the bacteria. How long will you be able to see the bacteria for? Does the bacteria disappear? If you would freeze the dish in the freezer, will the bacteria be maintained in the dish, still visible?





Keep in mind I'm only in grade 9 so keep it simple

How long does bacteria exist in agar?
Bacteria go through several phases: Lag phase, growth phase, stationary phase, and death phase.





Death phase is when the bacteria begin to die and it occurs when bacteria run out of nutrients (i.e. all the nutrients in the agar have been used up). You will be able to see the bacteria for as long as there are still nutrients present to sustain them. The bacteria do not disappear, they lyse (to put it in crude terms, they blow up). Some bacteria produce endospores, which are structures that can be subject to extreme conditions but still survive. These can give rise to more bacteria if you give them nutrients and a favorable environment.





If you freeze bacteria, they will form spores if they can but otherwise they will probably die depending on what kind of bacteria you're using. You can genetically modify bacteria in many ways to make them more cold resistant. There are also bacteria that naturally survive in extreme heat or cold. You will likely still see the colonies but the bacteria may be dead.
Reply:exactly! first poster is right on.... after all the starches/nutrients are used up (eaten by the bacteria).... the colonies will begin to die off... they will still be visible on that agar plate or tube, but they will be dead.





The cold tolerant bacteria that the first poster mentioned are called "psycrophiles" in microbiology.. and any bacteria that can live in Cold, or hot conditions and thrive are collectively known as "extremophiles". Hot loving bacteria are called "thermophiles"


There are other types as well... in case you were interested.


Iron-loving bacteria are known as "siderophores" and salt loving bacteria are called "halophiles".
Reply:If your goal is to keep the plates for a long time and still be able to see the colonies, it's pretty simple.





Once the colonies are at a size you can easily see, seal the edges of the petri dish closed so the agar inside won't dry up. (Parafilm or some stretchy tape works best, but any kind of tape will work if you do a good job %26amp; ensure there are no gaps.)





Then put the plate in the refrigerator (not the freezer). I'm not sure how long it will last like that, but I'd guess at least a year. As the other posters said, many of the bacteria may die, but you'll still be able to see the colonies.





Remember to keep the plate upside down while it's in the fridge. Otherwise, drops of condensation may form on the lid and drop down onto the agar surface. That will mess up the colonies.