UV mutagenesis and photo repair

Scientific concepts / nature phenomena presented

• UV mutagenesis (UVC)

  • Cells (Haloferax volcanii) are exposed to UVC light for controlled time intervals to induce DNA damage/mutations.
  • The experiment uses multiple exposure durations (e.g., 0, 15, 30, 45 seconds) to compare survival and mutant outcomes.

• Photo repair / light-dependent DNA repair

  • After UVC exposure, one condition is additionally exposed to visible light or sunlight (“Le” vs “no Le”).
  • This tests whether light can reverse some UV-induced DNA damage.

• Controls for light vs no light

  • Plates are labeled as:
    • no Le = no additional light exposure (dark control)
    • Le = exposed to light (photo-repair condition)

Methodology / procedure outlined (protocol)

Prepare materials

• Master plate of H. volcanii
• Agar plates (labeled)
• Exposure box with a UVC bulb
• Incubator (~45 °C) or a room-temperature alternative
• Sterile tools (e.g., Q-tips) and protective eyewear
• Saran Wrap and aluminum foil (to control light exposure)

Label agar plates

• Divide each plate into quarters
• Assign exposure times (example shown): 0, 15, 30, 45 seconds
• Mark each plate sector/plate with either:
  • no le (dark)
  • le (light/visible exposure)

Transfer cells from the master plate

• Scrape colonies from the master plate using a Q-tip
• Streak/spread evenly across the test agar plate (rotate the plate for uniform distribution)

Control which sectors receive UV

• Seal/cover the plate with Saran Wrap (tighten to minimize wrinkles)
• Keep all sectors covered except the specific sector being UV-exposed at that time

UV exposure

• Place the plate in the center of the exposure box
• Example timing shown:
  • Expose one sector for 15 seconds
  • Cover/remove lid as appropriate
  • Expose another sector for another 15 seconds (total 30 seconds)
  • A 45-second exposure condition is also demonstrated

Incubation

• Incubate after exposure:
  • At ~45 °C: about 4–5 days
  • Without an incubator (room temperature): about 2–3 weeks
• After incubation, compare outcomes between:
  • UV-exposed sectors
  • light vs no-light (“photo repair” vs control)

Featured researchers / sources

No specific researchers or external sources are named in the provided subtitles.