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Name: Martha
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Question:
For my biology class we did a lab that had to do withb DNA. To find the DNA we used lima bean bacteria. Now we are trying to find what bacteria is in lima beans. If you could help me out I would be very greatful.



Replies:
Martha, can you explain the experiment in more detail? Plants contain DNA as well, so how are you sure you isolated DNA from bacteria and not from the plant? What part of the plant did you use, or was it the bean itself? Did the bacteria come from the inside or outside of the lima bean? I need more information to answer your question.

Trudy Wassenaar


Lima Bean Bacteria Suspension: We place 1-2 handfuls of dry lima beans in a large jar and fill halfway to the top with distilled water. Then, covered and sat in a warn room for 2-3 days. After the 2-3 days we took one mL of the juice it produced and mixed it with different detergents. To find more about this experiment you can go to

http://www.accessexcellence.com/AE/newatg/Hayes/bacteria.html The lab at this web sight is very similar to the lab we performed. I hope this will help you in finding the bacteria in lima beans. Thank You Again,
Martha

Dear Martha, I understand your experiment better now. Let's follow the life of those Lima beans step by step. When they were inside their pod, they were sterile. When they came out, they no longer were, they must have been covered by bacteria present in the air, on the soil, on our hands, etc.

You took these beans and put them in sterile water with sugar. Then you left it grow. The bacteria present on those beans must have loved it and started to multiply. But, unless you made all precautions to keep the inside of the bowl sterile (tight, sterile lids, etc.) those bacteria that fly over will have landed in your soup and started growing there as well. So I think what you were culturing will have been a mixture of soil bacteria, skin bacteria, and the odd one flying by. I am afraid I can't tell you which of these will have multiplied best, for the ones that were there in highest numbers will have resulted in the most DNA.

In real-life lab work (if you like these science classes you may want to become a microbiologist) we want to be sure that we work with one type of bacteria only. This is what we would do to investigate this: From the sugar water after it had grown, we would take 0.1 ml and spread this on a sterile agar plate. We would also dilute the solution one to 10 and 1 to 100 with sterile water and plate out 0.1 ml of tose dilutions on two more agar plates. These would be incubated at 37 C untill we see bacterial colonies. From the size, shape and color of the colonies you can see if they are only one type, or if there are several types. If there are too many colonies present to judge, you use the plate from the dilutions that grows less colonies. Then we would take one pure, single colony, and spread this out over a fresh agar plate. Now we can be sure that all bacteria that grow there mst be the same. We would isolate DNA from the bacteria that grow on that final plate.

Maybe you can suggest to your teacher to do the first part of the experiment to see how many different kinds of bacteria were growing from your bean soup.

Good luck in science!

Trudy Wassenaar.



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