(4) RRR/T & RTR/R XIN Results 

Riya D -

This week’s results really threw me for a loop! 

Hypotheses: Since both trials have R2 (the low nutrient media) in that pre-UV stage, I think that the bacteria will have less energy to maintain their DNA repair mechanisms and will thus yield little to no radiation resistance under all UV levels (5, 15, and 25 mW/cm2). 

RRR/T 

  • Procedure: Though I had inoculated 4 flasks with D. xinjiangensis, only two of the inoculations went through: Samples A and C. So, this trial only had biological duplicates. 
  • Results:
  • Analysis: Concurrent with my hypothesis, these D. xinjiangensis had no growth under any of the UV levels! There was a little growth on the sample A section plated on R2A at a UV level of 25, but it was gram stained and found to be contamination, not D. xinjiangensis. 

RTR/T 

  • Procedure: Since this trial had different media in the pre- and during-UV stages, I had to perform a triple wash. To do so, I spun down each of the samples after taking the OD and immediately resuspended them in PCR water. I did that twice. Then, for the last wash, I resuspended them in TGYB before exposing them to UV. 
  • Results:
  • Analysis: Surprisingly, all the plates had growth, thereby refuting my hypothesis! And, it doesn’t even look as though the growth was diminished too harshly as the UV level increased. 

As this week showed, it appears that it is in fact that during-UV stage that matters the most when it comes to D. xinjiangensis’s resistance: when the bacteria is exposed under TGY, they are quite resistant, yet when they are under R2, their resistance greatly diminishes. 

Next week, I look forward to conducting that last trial, TRT/R, to confirm this new hypothesis! 

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Comments:

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    sudeep_v
    With any microbiology wet-lab experiment, the risk of contamination by other bacteria is always present. Have you experienced any bacterial contamination yet (Staphylococcus aureus?). If so, how do you limit it?
    March 18, 2025 at 3:59 pm - Reply
    Anonymous
    Yes, this project has had its fair share of contamination, particularly this dark yellow contaminant as you can see on the RTT, UV=5, Sample C. From the gram stains, it does not appear to be Staphylococcus, and honestly I do not know what it is. However, to limit it, I sterilize the parafilm under UV before I expose the XIN, I try to plate in the hood as much as possible, and I always ethanol down before I do any work inside the UV box. Thankfully, as my project has progressed, I have been able to greatly reduce the amount of contamination I've seen!
    March 20, 2025 at 1:54 pm - Reply
    riya_dh
    Yes, this project has had its fair share of contamination, particularly this dark yellow contaminant as you can see on the RTT, UV=5, Sample C. From the gram stains, it does not appear to be Staphylococcus, and honestly I do not know what it is. However, to limit it, I sterilize the parafilm under UV before I expose the XIN, I try to plate in the hood as much as possible, and I always ethanol down before I do any work inside the UV box. Thankfully, as my project has progressed, I have been able to greatly reduce the amount of contamination I’ve seen!
    March 20, 2025 at 1:55 pm - Reply

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