Wolbachia: Discover the Microbes Within

The final lab of the year was about Wolbachia. This lab was super interesting and a great summary of the content and lab skills we have learned throughout the whole year!

Purpose

The purpose of this lab was to determine whether or not bugs collected from students’ surrounding areas are infected with Wolbachia. By doing this, the goals were to investigate and observe the effects of Wolbachia on insects and insect populations. During this lab, we were able to learn about symbiotic relationships among organisms and use our lab skills to analyze DNA and determine the closest match to a given DNA sequence using bioinformatics.

Introduction

Wolbachia is a bacterium that infects arthropods and it is present in over 60% of all insects. Wolbachia is passed from parent to offspring through the female’s eggs. Therefore, to increase its chances of transmission and being passed on, Wolbachia changes the sex of its host to female, this is called feminization. Feminization greatly reduces the number of males in a population, ensuring that Wolbachia keeps being passed on to the next generation in greater abundance. In some species, Wolbachia can cause females to reproduce parthenogenetically, meaning a female can reproduce without a male partner’s sperm and her offspring will be identical copies of her. In other species, infection with Wolbachia causes all offspring to develop as female, no matter the actual genotype of the individual. Still, in other species, Wolbachia causes male embryos to abort in early stages of development.

Wolbachia is being studied because it can be used in many positive ways. First of all, Wolbachia is safe for humans, other animals, and the environment. Currently, studies are being conducted that show that introducing Wolbachia to mosquito populations can prevent harmful viruses, such as Dengue Fever, Yellow Fever, Malaria, and Zika Virus, from growing inside mosquitos and being transmitted to humans. This is a huge breakthrough in the study of viruses and human health!

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Photo from the Eliminate Dengue Program.

 

Wolbachia’s relationship with insects is one of parasitism because the parasitic bacteria Wolbachia live inside the reproductive organs of the host. However, the relationship between Wolbachia and filarial nematode hosts is one of mutualism because both organisms benefit from the interaction. The effects of feminization greatly alter and distort the ratio of males to females in insect populations. Both the total number of offspring and the genetic diversity are reduced by Wolbachia.

 

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Photo from the Eliminate Dengue Program.

 

Techniques

To screen for Wolbachia in insects, the techniques used were DNA extraction, Polymerase Chain Reaction (PCR), and Gel Electrophoresis. First and foremost, students collected and brought in arthropods frozen in alcohol. Then, DNA extraction extracted and separated the DNA from the arthropod cells. PCR targeted and amplified two regions of the DNA: an insect region, which is present in all insects, and a Wolbachia region, present only in insects infected with Wolbachia. PCR made many copies of these specific sections of DNA. Next, gel electrophoresis visualized the results by separating normal insect DNA from Wolbachia DNA in each sample. This showed either the presence or absence of the Wolbachia region of DNA for each arthropod.

Results & Analysis

Here are the results from the lab!

*insert pictures of gel electrophoresis*

Our results show that 4 arthropods among the collected samples were infected with Wolbachia. These arthropods that tested positive for Wolbachia were from San Carlos and Redwood City, which supports that other insects in these areas most likely are infected also. Something interesting about our results is that the negative results came from areas farther away from the San Carlos/Redwood City area.

Data from the California Wolbachia Map shows that the prevalence for Wolbachia in Beetles is 20%, which is interesting because my beetle tested positive for Wolbachia while the other beetle sample collected in our class tested negative. So from our class’ data alone, one might conclude that Wolbachia is present in 50% of beetles, but looking at a larger test taken from more samples, one would see that the prevalence rate is actually not as high as 50%! Likewise, according to the California Wolbachia Map, the prevalence rate of Wolbachia in tested arthropods is 40.741% in San Mateo and 18.75% in Redwood City. The rate in our class’ experiment was 4/11 or about 36%, which is lower than the accepted rate of Wolbachia infecting over 60% of all insects. Keep in mind that our class data is taken from a very small and limited range of samples.

Experience

The experience of this lab was really great. It perfectly summed up all of the lab skills we have been learning about this whole year. We had to know about the structure of cells and DNA in order to understand how DNA extraction and gel electrophoresis would work. We had to understand the processes of DNA Replication to know how PCR worked. I feel like all of the labs we have done over our time in AP Bio have been preparing us for this lab! Following directions and making sure to pay attention to details was important, especially when dealing with something as particular, specific, and fragile as DNA.

I feel confident in my lab skills because I was able to get not only a result from the gel electrophoresis but also get a positive result! This means that I was able to successfully extract the DNA, follow the directions, and show that my bug, which was a beetle, was in fact infected with Wolbachia.

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