Science Buddies: "Ask an Expert"

Hi for a biology experiment I want to grow probiotics (Lactobacillus GG) in a liquid nutrient broth. This is because I want to measure the bacterial growth by the turbidity of the liquid. The variable I am changing is the salinity of the solution.

Any ideas on the best to do this !!

Thanks, Hannah

Hi Hannah,

Here is information on MRS growth medium, which was optimized to support the growth of Lactobacillus species. The medium is high in protein and glucose, and has a slightly acidic pH. The recipe has several ingredients, so if you can’t get this medium or the ingredients, let me know and I will suggest possible alternatives. The growth medium is one of your controlled parameters, so should be the same for all samples For liquid samples, you would omit the agar.

https://en.wikipedia.org/wiki/MRS_agar

If you have not grown bacteria before, please do review information on microbiological techniques from the website:

https://www.sciencebuddies.org/science- ... ques.shtml

I have a question for you. What is the reason that you want to vary the salt concentration? What are you trying to show?

Let us know if you have any other questions.

Donna Hardy

Thank you so much, Donna Hardy
I am changing the salt levels to see how salinity affects the growth of bacteria. I think I will make a salt buffer of water and salt and mix it into the liquid medium.

Hi,

Thanks for the explanation. It sounds like you have planned a very carefully controlled experiment.

I wanted to make sure that you also have a purpose for doing a project on the effect of sodium chloride on the growth of lactobacilli.

For example, here is a link for a paper that reports the results of sodium chloride on the growth of Lactobacillus.
http://www.csub.edu/~kszick_miranda/fer ... t%20al.pdf

If you read the introduction, you will understand that the authors were investigating how to improve the quality and consistency of sourdough bread. For your project, it will be helpful if you had a reason for doing your experiment. The purpose might be to improve sourdough bread, or some other food application. You could include thia n in your background information.



Donna