Lab 23: Physical Methods of Control: UV Radiation

nonionizing

1. essential for biochemical processes 2. main absorption wavelengths for algae, green plants, and photosynthetic bacteria 3. animal cells synthesize vit. D in the presence of light 4. around 300 nm

ultraviolet (UV)

1. nonionizing radiation between 15 and 400 nm 2. wavelengths below 200 nm are absorbed by air and don't reach living organisms

ionizing radiation

1. radiation with enough energy to free electrons from atoms forming ions 2. may cause cancer (ex. gamma, X-rays, UV) 3. ionize water

thymine dimers

1. ultraviolet light induces them in DNA 2. cause mutations

radiant energy spectrum

1. uninterrupted band or continuous spectrum of visible and invisible light that ranges from short to long wavelength 2. includes gamma rays, X rays, microwaves, and visible light

What are the variables in ultraviolet radiation treatment?

1. wavelengths 2. time 3. distance 4. light/dark incubation

Why are there still some colonies growing in the areas exposed to ultraviolet light?

After ultraviolet light indices thiamin dimers in DNA they result in mutation. Incubation in dark or light can repair the DNA(light or dark repair)

Many of the microorganisms found on environmental surfaces are pigmented. Of what possible advantage is the pigment?

Can absorb different frequencies of light and uses it as energy or protection

S. marcescens results

Cover: Foil Control growth: +4 30 sec. UV exposure/dark incubation: +4 30 sec. UV exposure/light incubation: +2

B. subtiilis results

Cover: Gauze Control growth: +3.5 30 sec. UV exposure/dark incubation: +2 30 sec. UV exposure/light incubation: +3

St. epidemermis results

Cover: Gauze Control growth: +4 30 sec. UV exposure/dark incubation: +3 30 sec. UV exposure/light incubation: +2.5

Considering your results,discuss the possible effects of UV radiation on the ecology of a lake if the UV radiation has the same effect on the lake bacteria as it did on the bacteria in your experiment.

In the lake, plants can survive better in UV radiation because they can absorb the wavelengths.

How might the results differ if a UVA lamp were used? A UVB lamp?

UVA's are not easily absorbed therefore are less active It does not penetarte the cell as well it would not be effective in killing bacteria. UVB lamps cause damage to DNA killing bacteria

If the Bacillus had sporulated before exposure to radiation, would that have affected the results?

Yes, the spores can withstand extreme conditions

highly reactive free radicals

ionized water that can break strands of DNA (unpaired electrons)

UVB wavelengths

1. 290-320 nm 2. cause damage to DNA

UVA wavelengths

1. 320-400 nm 2. not readily absorbed 3. less active on living organisms

Procedure

1. Swab culture on both halves of Petri dish (2 dishes) 2. You will have a control and test portion of plate 3. Cover control and expose to UV light 24 cm from light, lid off, agar side up 4. one plate will be exposed to natural light, second plate will be placed in dark environment 5. examine growth on organisms on day 2

sterilizing

1. UV radiation is limited due to poor penetration 2. sterilize some heat-labile solutions, decontaminate hospital operating rooms, food-processing areas, and disinfect water

photolyases

1. activated when thymine dimers are exposed to natural light 2. split dimers 3. restore DNA 4. light repair or photoreactivation

UVC range

1. biocidal 2. 200-290 nm 3. correspond to the optimal absorption wavelengths of DNA

dark repair

1. dimers are removed by endonuclease 2. DNA polymerase replaces the nucleotides, and DNA ligase seals the sugar-phosphate nucleotides