Fingerprinting the Culprit

— Written by Vivian Lee


Figure 1. Sea star tube feet sample in 100% ethanol

What are some things that come into mind when we think of DNA fingerprinting? Perhaps, an episode of CSI or Criminal Minds about identifying a murder suspect might be the first thought that crosses our minds. Similar to finding a murder suspect, bacteria DNA fingerprinting is being studied in my lab with Dr. Nguyen to catch a possible culprit, a bacterium known as Vibrio, which may be responsible for the sudden deaths of sea stars that occurred across the West Coast in 2014. In hopes of finding the presence of Vibrio on sea stars, we will culture the bacteria on plates in different agar environments, some that are rich in nutrients more than others to grasp how this bacterium behaves in the ocean, and the effects that it harbors on sea stars in the Rocky Intertidal.

Let’s take a step back and sink ourselves into an episode of a crime investigation scene where there is a case investigator and a crime scene personnel collecting sources of evidence such as hair or blood, swabbing around the perimeter to collect any other possible articles of DNA to then have it analyzed in a lab. Likewise, I play a similar role in which I collect DNA of sea stars out in the field, to then have the DNA extracted, whereupon, an amplification is done through Polymerase Chain Reaction (PCR). Once the fragments of DNA are separated by gel electrophoresis, I observe the fragment size to


Figure 2. Species Pisaster ochraceus found

analyze the presence of the 16s ribosomal subunit. This gene prompts the identification of a bacteria present in a bacterium swab sampled from a sea star. There are two methods in which DNA and the presence of multiple bacterial communities are collected from the stars. One, where I bargain with the sea stars as they give me a fair game of tug of war with their tube feet and when I win, in exchange I take a few tube feet back to the lab as seen in Figure 1. These organisms have the capability of regenerating their tube feet, as well as their arms, which allows the methodology of stealing their tissue quick and convenient. Because sea stars possess this trait of restoration to heal damaged tissues, questions arose when these Echinoderms began “melting”, one arm at a time when they became infected with the Sea Star Wasting Disease. Secondly, to observe which bacterial communities place sea stars under huge amounts of distress, areas where white lesions form on the body as seen in Figure 2 are swabbed, along with the exterior tissues that do not have white lesions, therefore to compare the presence of Vibrio in “healthy” and “non-healthy” sectors of the body.


Figure 3a. Coal Oil Point Rocky Intertidal. b. Emma Saas and Vivian Lee making observations at Hazards Canyon intertidal. c. Species Pisaster ochraceus affected by SSWD

Sampling the species of Pisaster ochraceus non-local sites such as Hazards Canyon in comparison to the local intertidal at Coal Oil Point, where it has become barren of sea stars raises questions concerning to what is holding one species over another back from making a comeback to recovery. By surfacing one of many hypotheses proposed about the cause of the Sea Star Wasting Disease through observing past bacterium samples that were collected during the Sea Star Wasting Disease is currently preparing me to compare the presence of the 16s ribosomal subunit in current stars that may have survived the disease.

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