Protocol Online logo
Top : Forum Archives: : Biology Science Fair Projects

What type of agar is best to grow my bacteria? - Sceince fair project on leaf bacteria, can someone help (Dec/01/2005 )

Pages: Previous 1 2 

Thanks everyone for your input. However i'm not sure if the way i stated anything made it sound as though i thought that there was only bad bacteria on the outside of the leaf because i do know that there is both good and bad bacteria on the leaf. The reason i was wanting to look at the inside of the leaf is because i would have to isolate the two types of bacteria before doing any type of testing on the helpful bacteria. the bacteria on the inside would make sense that it is the bacteria protecting the leaf against any pathogens from entering into the leaf. This website may clarify what i am trying to say:

Are there Gaurd-Dog Bactria in Leaves?

I'm not sure if i posted this website correctly because i'm new to this. I hope it works!
I think that Redwalar has already looked at this site or one similar and has given me very helpful input on this. Thanks Redwalar!
I agree with you homebrew, i do need to set up a hypothesis before starting this expirement. I have talked to my AP biology teacher about what i found and i need to modify the procedure in order to make it my project and not just something that has been taken form the internet. So that this will be my own work. My AP bio teacher said that he can provide me with some of the equipment that i need so I have something that i can work with for what i want to do.
thanks again everyone

-lou lou-

Okay, good! So let's get to work on devising your experiment to get the most bang for the buck...

I was glad to see the website you linked to ends with "But are they guard dogs...?", because just culturing bacteria from the inside of the leave says nothing about any mutualistic role they might play with the plant. They could, after all, just as easily be plant pathogens that have successfully invaded the plant, right?

So let's say you get a population of bacterial isolates from inside the leaf. There are likely to be several different species represented. Where might you get a population of bacteria to which these are antagonistic?


QUOTE (HomeBrew @ Dec 3 2005, 12:22 PM)
So let's say you get a population of bacterial isolates from inside the leaf. There are likely to be several different species represented. Where might you get a population of bacteria to which these are antagonistic?

ok well when you say antagonistic does this mean an organism(bacteria) that is interfering with the plants way in which it prevents harmful bacteria from entering?

-lou lou-

oh ok i understand now, what i would be doing probably is testing each of the cultures that develope in relation with some of the harmful bacteria on the outside of the leaf in order to see whether or not they really are preventing any growth of the harmful pathogens or if they are just present inside the plant.

-lou lou-

again, your hardest two questions (these need to be dealt with long before you worry about how to ID the bacteria you get) are this: to get bacteria from inside that are 'good' for the plant to differentiate bacteria that are good or bad on the outside of the plant

looking at antagonism is pretty easy, I can send you a method for that from a general microbiology course (this is a way to show if some of the bacteria can inhibit growth of other bacteria); the only hard part is finding an appropriate media to use

but you need to be able to differentiate between the good and the bad.

here is something for you to consider:

get a good organic gardening book for your area, with pictures of bacterial diseases and hopefully with something identifying the bacterial types that may be involved. go find a couple plants in your yard (or a park nearby, or at your neighbor's place; make this easy), next to each other, if you can (same soil is a better control)...where one appears to be sick with a bacterial illness, and one appears to be healthy. culture what you get off the leaves of each. set up an antagonism experiment with the isolates you get from the healthy plant, against the pathogen. see if any of the healthy-plant isolates antagonize the possibly-pathogenic organism.

another thing to consider, that would be a good experiment for a science fair, is that sometimes these relationships can exist between fungi and bacteria on the plant. consider how many antibiotics were first isolated from fungi??? you may be able to isolate a fungi or two from a healthy plant, then get some known bacterial plant pathogen or two (your local university may be able to help) and set up an antagonism experiment.

some resources for you, beyond your biology teacher, could be your local gardening clubs, master gardeners if they are in the area, county extension programs regarding local plants, nurseries...places like this. For example, where I live there are workshops put on by master gardeners to help people identify and combat plant diseases in their gardens. master gardeners are also required to spend a certain amount of time volunteering in the community every year. if you could team up with someone like this as a mentor, you may get a lot of valuable help and resources. most communities that are not really small would have such programs in place, and if you can't find the available contacts on the net, then you could ask at a local nursery. those places are usually more than happy to provide all sorts of information

good luck with your project


Yes, now we're moving toward a science fair project worthy of a BioForum member... biggrin.gif

Yes, lou lou, I was thinking of pitting the population of bacteria found outside the leaf against those found inside the leaf. The problem is how to do it, since we have no way in the mixed population to differentiate between bugs that were on the outside and bugs that were on the inside.

I know nothing about this phenomena, but I suppose it's possible that the nature of the defense is products secreted by the guard bacteria. Were that the case, you might be able to show killing of the outside bacteria by growing inside bacteria in liquid media, centrifuging them out, filter sterilizing the spent media, and adding it to a growing culture of outside bugs...


homebrew, I still think streaking to show antagonism is by far the easiest are looking at inhibition by conditioned medium; that's an awesome idea but I cant' see it happening in a science classroom

All you need for antagonism are some petris and some bugs that are aerobic, with an incubator

that's another issue! if in fact there are bugs inside the leaf, would they be able to grow under aerobic conditions?


I like the sound of the antagonism method but it wouldn't hurt to hear about the inhibition by a conditioned medium. if all i need is a centrifuge we have one at our high school. maybe you could tell me a little bit more about the inhibition idea just so i know what you're talking about, it may be a possibility that i wouldn't want to rule out.
Thanks for all of your help. Not only am i getting my project set up but i am learning a lot more than i knew.
Oh and thanks aimikins, i'll let you know tomorrow about the information on antagonism. I would really like to get that information as soon as i can. I'll check with my teacher and see if it is ok. Thanks again.

-lou lou-

Hi everyone,
i haven't been on lately because of exams and i have been doing some individual research on my project. But addressing my question: aimikins, how can i tell if the bacteria are areobic or anaerobic? is there some sort of quick and simple test that i can do. And i'd still like to hear homebrew's previous idea because if i can do that regardless of wether or not the bacteria need oxygen then would that not save me from any future problems or does the antagonism experiment take care of both aerobic and anaerobic bacteria?

-lou lou-

To my knowledge, there is no 'quick and simple' test...short of growing them up. anything that dies, is anaerobic... blink.gif

I would think perhaps you should limit yourself to bacteria that are aerobic. I still think your best bet will be bacteria on the outside of the leaf, but I am no botanist....think of it this way: you are looking for bacteria that tool around on the plant, perhaps making some compounds beneficial to the plant that might repel or kill invading organisms. for these bacteria to spread through a plant population, in order to be very effective they would have to be able to live in ambient air. think about the BT example; some of the reason B thuringensis is such an effective aid to the plant is that it can spread itself pretty readily in the environment. So, if I were you I would make life much easier and go for microbes that can grow aerobically.

It really depends on what exactly you want to show...I can only tell you how I would do it, but there are many ways to design an experiment and it is ultimately up to you. I would grind up and culture a few leaves (perhaps from a couple different species of plant) and set up an antagonism experiment with the growth you get against some common plant pathogens. I think the conditioned medium approach is valid, but may end up being more difficult in the long run.

What exactly do you wish to show? that is always the place to start smile.gif


Pages: Previous 1 2