Wolbachia Mania!

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Purpose: To find out if the bacterium Wolbachia is present in arthropods and insects found in our surroundings.

 

 

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Wolbachia. Photo courtesy of eliminatedengue.com

 

Introduction: Wolbachia is a highly successful genus of bacterium that is present in an estimated 65% of all insects, or 1,000,000 species. Wolbachia differs from other types of bacteria because it infects and enters individual cells, not just areas of a body system.

Wolbachia is a highly successful genus of bacterium that is present in an estimated 65% of all insects, or 1,000,000 species. Wolbachia differs from other types of bacteria because it infects and enters individual cells, not just areas of a body system.

Wolbachia is a highly successful genus of bacterium that is present in an estimated 65% of all insects, or 1,000,000 species. Wolbachia differs from other types of bacteria because it infects and enters individual cells, not just areas of a body system. Inside the cell, Wolbachia latches onto the spindles that are used during mitosis in order to spread through cell division. Even after a week of the host’s death, Wolbachia can survive in the host’s cells.

Wolbachia is only successfully passed on in female hosts, so the bacterium has several adaptations that alter the sex of its host and the host’s offspring to ensure the success of the bacterium’s genes.

One way is by cytoplasmic incompatibility. If there is an infected male, his sperm cannot fertilize an uninfected egg because the sperm does not condense the chromosomes entirely. However, infected eggs can be fertilized by either infected or non-infected sperm. This ensures that the Wolbachia has female hosts to survive in. Another way of reducing the male population is by ensuring the chromosomes double after the parthenogenesis of gametes. Many insect males have one set of chromosomes because they originate from an unfertilized egg. Female insect offspring originate from fertilized eggs and have two sets of chromosomes.

 

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Cytoplasmic incompatibility. Photo courtesy of nature.com

 

Another way of reducing the male population is by ensuring the chromosomes double after the parthenogenesis of gametes. Many insect males have one set of chromosomes because they originate from an unfertilized egg. Female insect offspring originate from fertilized eggs and have two sets of chromosomes. Wolbachia forces unfertilized eggs to double their chromosomes to create females instead of males.

Other times, Wolbachia destroys the organs that create male sex hormones, and the offspring transform into females.

Because Wolbachia has such fascinating features, scientists want to use the bacterium to prevent the spread of malaria. Malaria is caused by a protozoan and is transmitted only through female mosquitoes. Scientists are attempting to insert the protozoan-resistance gene into the Wolbachia genome, for the Wolbachia then infects female mosquitoes. The female mosquitoes would theoretically not pick up the protozoan because of the protozoan-resistant gene. Because there would be no qualified vector, malaria would stop spreading in humans.

However, Wolbachia does not infect the mosquito Aedes aegypti, a major vector of Dengue fever. Scientists are researching why this is, as some genetic engineering could change the future of the disease.

Lab Techniques:

Three major steps were taken to examine if Wolbachia DNA was present in the insects and arthropods collected: 1) extraction, 2) PCR, and 3) gel electrophoresis.

The purpose of the extraction was to isolate the DNA from the rest of the insect. This required Team AP Bio to collect insects, cut off abdomen, where the reproductive structures are (and where Wolbachia infects), and separate the DNA from the rest of the parts of the insect. The insects sat in alcohol before being crushed, spun with a lysis buffer, heated, and cooled. I was absent for the PCR, but I still understand the basic steps. The purpose of the PCR, or polymerase chain reaction, is to multiply copies of a small, specified section of DNA so the section is visible for sequencing and other lab uses. PCRs require DNA, primers that indicate where the desired DNA fragment begins, the DNA polymerase enzyme to make copies of the desired fragment, and nucleotide base pairs for the DNA polymerase to make new DNA fragments with. The samples are placed in a thermocycler that changes temperatures at specified times to split the DNA (heat shock), put the primers in place (cool), and allow DNA polymerase to replicate the fragment (slightly cooler the heat shock).

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DNA extraction. Photo courtesy of labiotech.edu

I was absent for the PCR, but I still understand the basic steps. The purpose of the PCR, or polymerase chain reaction, is to multiply copies of a small, specified section of DNA so the section is visible for sequencing and other lab uses. PCRs require DNA, primers that indicate where the desired DNA fragment begins, the DNA polymerase enzyme to make copies of the desired fragment, and nucleotide base pairs for the DNA polymerase to make new DNA fragments with. The samples are placed in a thermocycler that changes temperatures at specified times to split the DNA (heat shock), put the primers in place (cool), and allow DNA polymerase to replicate the fragment (slightly cooler the heat shock).

 

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PCR. Photo courtesy of abmgood.com

The gel electrophoresis was the final procedure in the lab. The purpose of the electrophoresis was to separate and identify the insect DNA from the Wolbachia DNA. All of the PCR samples placed in wells of a gel electrophoresis box on the negative side, and electricity ran through the gel and moved the DNA towards the positive end of the gel (DNA is negatively charged and therefore attracted to the positive end.) A ladder was used to show exactly where the insect and Wolbachia DNA should line up after the gel was run. Different fragments of DNA at different spots show how big (how many base pairs) the fragments were, and the size is used to identify what the fragment codes for.

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Gel electrophoresis tank. Photo courtesy of yourgenome.org

 

Results:

The results of the electrophoresis were analyzed in class. A pattern observed was that insects and arthropods from San Carlos were infected the Wolbachia bacterium, while those from north and south of San Carlos (Burlingame, Brisbane, Palo Alto) were not infected.

The Experience of a Complex Lab:

Although I was absent for the PCR, I still benefitted from experiencing the laboratory procedures. I have never been a fan of labs and experiments because I feel like I will miss a step or do something wrong. To make sure I don’t make mistakes on such detailed steps, I proceed slowly, but this makes me fall behind all my classmates and miss the checkpoints that we need to meet as a class.

Despite my fears, using the biotech tools was very fun and made me feel very professional! I love ejecting the micropipette tips into the waste beaker, loading the electrophoresis gels, and spinning the mini samples in the vortex machine. I know I’ve definitely improved since sophomore year biology when I was afraid of practically everything in the lab. I know I’m one step closer to mastering lab procedures in college!

 

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Me in ten years! Photo courtesy of dataev.com

 

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One thought on “Wolbachia Mania!

  1. Edith Leung

    You guys definitely put the AP in AP Biology! This seems like such complicated, college-level laboratory work. I can imagine you guys with goggles and a white lab coat like the scientists in movies.
    I had no idea a bacteria like Wolbachia existed. It’s crazy that they can manipulate the gender of the insect children and insects themselves. Is there any way Wolbachia could change human genders too? Can you imagine how insane that would be? That would easily become the focus of the medical world.
    It’s cool how you all used the PCR and electrophoresis equipment! I’m jealous, I did not get to do this in high school!

    Liked by 1 person

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