Experiment 17: Effect of UV Radiation

which bact are harmed by UV radiation?

most, except photosynthetic bact

what UV wavelenghts cause non photosyntheitc bact to be damaged?

short UV wavelgnths of 210-300nm

how is UV used to sterilize?

causes peroxides to form which act as oxidizing agents producing germidical effects like nucleic acid mutations or abnormal linkages btwn bases

ex. T binds. w/ another T = thymine dimer = abnormal protein = prevent replication = lethal unless repaired

greater # of UV radiation absorbed =

greater # of mutations

longer exposure times to UV radiation results in what?

greater dmaage to bact cells and higher lvl of inhibition than veg cells bc endospores are protected by acid soluble proteins that protect the DNA from photochemical damage

does UV radiation affect endospores?

yea but less resistant than spore producing species like Clostridium or bacillus

enzyme systems in bact cells detetc what?

locate and repair damages sections of DNA

1. some are ohotoactivated repair systems, activated by light

   1. cleave covalent bonds that make the thymine dumers and resore DNA to og state without replacing the thymines

2. dark repaire systems dont need light to be activated

   1. cut thyine dimers out to replace them w new spearate thymines

Exp 17 learning objectives

1. asses lethality and mutagenic effects of UV radiation of veg cells and spores

2. understand mehcnaimd of UV damage

3. Compare UV sensitivity or resistance btwn species

exp 17 materials

1. UV lamp w wavelgnth of 200-300 nm

2. Staphcocculsu aureus

3. Priestia megatarium

4. poured nutrient agar plates

5. sterile swabs

exp 17 method

1. divide plate into 3 vertically and cut those in half (6 sections) label 0 0.5 and 1 min and other w 2 min 3 min and 3L (3min w lid on)

2. aseptically swab both plates w cultures, vertical streak motion.

3. remove lid, place on bottom of UV lamp tray 0 and 2 min section closest to u.

4. open both shutters quiclyk and slide twd u.

5. 30s — close left shutter until red line.

6. 1 min — close left shutter fully. first plate fully covered.

7. 2 min — close right shutter until red line.

8. 3 min — close right shutter fully.

9. incbuate at 37deg for 48hr

Results - Staphylococcus aureus

0s/control = (++++)

0.5 min = (++++)

1 min = (++)

2 min = (+)

3 min = (- - -)

3L lidon = (+++)

BEST = 0-0.5min

less resistance to UV = white yellow mutated colonies

Results - Priestia megaterium

0s/control = (++++)

0.5 min = (++++)

1 min = (+++)

2 min = (++)

3 min = (+)

3L lidon = (+++)

more resistant to UV = endospores