Science Buddies: "Ask an Expert"

In light of prophylactic antibiotics given to help prevent secondary infections in covid, I wondered whether killing the good bacteria might be harmful. Last year, I did a project where I knocked out the bacterial microbiome in bean plants. I then infected the plants with tobacco mosaic virus and found that the virus was more infective in the absence of a good soil microbiome. I won both our Colorado State and Pikes Peak Regional Fair’s grand prizes for middle school with this project.



This year, I am in 8th grade and I would like to look at an animal microbiome. Is there a way I could mimic a healthy human gut ecology in a Petri dish and subject it to a virus? I am considering ordering the Ward’s Coliphage Culture & Titer Determination Lab Activity. I would place the T4r phage on both a plate with a microbiome in the agar and one without. Could someone give me some scientific feedback on this? I want to know if this sounds like a feasible idea and what other ways I might possibly test the infectivity of a virus with and without a healthy microflora, not whether the safety committee will allow it. If they will not, I’ll seek out a college lab.



On another note: even though I won the fairs, I am also wondering how my project even worked last year, since I knocked out the soil & leaf bacteria. How did the virus replicate?


Thank you so much for the help.

Hello,

This sounds like a really interesting project idea! Let me start by answering your question about how the tobacco mosaic virus replicated without the soil and leaf bacteria. The tobacco mosaic virus infects plant cells, which damages them and hurts the plant. The virus does not infect bacterial cells, so it does not need bacteria to replicate.

Bacteriophages, on the other hand, are viruses that specifically infect bacterial cells. The T4r phage that you want to order infects E. coli cells. So if you plate E. coli on a petri dish and add the T4r phages, they should infect the bacterial cells. If you add the viruses to an agar dish with no bacteria, nothing will happen because they don't have any cells to infect. So doing this experiment wouldn't really give you any new information since we already know that T4r phages will infect and kill bacteria.

If a scientist wanted to test how virus infectivity is affected by the presence or absence of gut bacteria, they would probably use mice as an animal model for the study. They would take mice with a normal gut microbiome and mice that don't have any bacteria in the gut (what we call "germ free" mice), and infect the mice with a virus to see which group of mice does better. In your case, working with live animals wouldn't be feasible since scientists have to go through an extensive review process before they can get approved to do animal work. Working with viruses that can infect animals would definitely require a professional lab because there are many safety regulations that need to be followed.

This all goes to say that animal studies are a lot more complicated than plant studies, so you might have trouble doing an animal microbiome project. However, I don't think it's a bad idea to do a project involving phage viruses and bacteria. There's been a lot of talk about using bacteriophages to kill bacteria as an alternative to antibiotics, so that could be an interesting project to consider.

I hope this helped answer your questions. Don't hesitate to post any other questions that you have!