High Temperature and Ultraviolet Rays’ Effect on Different Types of Bacteria Report

Introduction

All organisms are made up of cells; they contain structures and perform functions that ensure the survival of all living entities. Nonetheless, they can be exposed to certain conditions that alter their functioning since they survive in specific environments. These conditions include high temperatures, low temperatures, exposure to certain chemicals, and even Ultraviolet radiation. High temperature above a cell’s optimum temperature for survival affects the structural composition of a cell. The plasma membrane (PM) is affected first since it is the outer boundary. It comprises a phospholipid bilayer containing fatty acids (F.A.) and integral proteins forming a mosaic. The components of this layer make it selective for molecules and ions, regulating substances that pass through it. Extremely high temperatures lead to reduced rigidity of F.A., changing the PM’s permeability allowing entry of materials that may be harmful to the cell, and denaturing Proteins that make up the mosaic. All organelles bound by a membrane are subject to these effects, which eventually cause apoptosis.

Ultraviolet rays focus on the cell’s DNA; exposure to U.V. rays causes damage either directly or indirectly. Direct harm occurs when photons of the U.V. rays hit the DNA molecule. It absorbs energy and becomes briefly excited, and it is during this excitation that two DNA base pairs of proximity can fuse and cause mutations in the structure. This alteration leads to changes in the functioning of the cell. Indirect harm is caused when an oxygen molecule (O2) comes into contact with U.V. rays and becomes unstable due to excitation. The O2, therefore, collides with any protein in the quest to dissipate the extra energy. If a collision occurs with DNA, transversion between guanine and thymine occurs, altering the DNA’s translation into protein. Consequently, mutations that are harmful to the functioning of the cell follow.In this experiment, cultured bacteria; Bacillus megaterium, Staphylococcus capitis, and Enterobacter aerogenes were focused on to see how increased temperatures and ultraviolet rays affected them. B. megaterium is a rod-like, aerobic gram-positive bacteria in common soils and some food such as honey. It survives in temperatures of 3◦C to 45◦C; however, its optimal temperature for functioning is 30◦C. It is also known to survive harsh conditions of up to 65◦C.

Staphylococcus capitis is an aerobic, gram-positive bacteria found on the normal flora of the skin- the scalp, face, neck, scrotum, and ears. The coagulase-negative bacteriocin exists between 6.5◦C to 46◦C with an optimal functioning being between 30◦C and 37◦C. ?’##Enterobacter aerogenes is a pathogenic rod-shaped, gram-negative oxidase-negative bacteria. It is found within the human gastrointestinal tract, in wastes, and some hygienic chemicals. It survives at temperatures ranging from 25◦C and 40◦C, 37◦C being its optimal functioning temperature.

The following is a list of hypotheses made concerning this experiment:

• If B. megaterium is exposed to 100 degrees Celsius and U.V. light, then the cells will form endospores and survive the harsh environment to protect the cells.
• If S. capitis is exposed to 100 degrees Celsius and U.V. light, the cells will expand and not survive.
• If E. aerogenes is exposed to 100 degrees Celsius and U.V. light, then they will survive in water and air because they are facultative anaerobes.

Materials and Methods

The experiment was done in groups of three using inoculations of Bacillus megaterium, Enterobacter aerogenes, and Staphylococcus capitis.

In boiling water

Materials

• A can
• One tube of nutrient broth
• One cotton-tipped swab, each labeled with the student’s three initials using wax pencils, obtained from the media cart.

Methods

1. The group’s working cultures were obtained from the instructor.
2. The swab was used to inoculate the broth with the working culture. It was transferred to the broth tube and closed within with the lid. The lid was then labeled with the organism’s initials and the boiling time frame and boiled for 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, and 30 minutes.
3. The inoculated broth was placed into boiling water for the appropriate time, then removed using test tube holders and incubated.
4. In the next lab period, growth was evaluated, and results were placed into the table.
5. The cultures were then disposed into a biohazard bag labeled “Glass only.”

U.V. Light

Materials

• One plate of nutrient agar
• One cotton-tipped swab, obtained from the media cart, each labeled with their three initials using a wax pencil.

Methods

1. The group’s working cultures were obtained from the instructor.
2. A line was drawn down the middle of the plate, and one half was labeled “A” and the other half was labeled “B.”
3. The swab was soaked in the working culture, and a confluent plate was made by completely covering the plate with a streaking pattern to inoculate the working culture.
4. The lid was labeled with the organism’s initials and the U.V. light time frame for exposure: 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, and 30 minutes.
5. The lids of the Petri plates were then replaced with square paper.
6. The inoculated plates were placed on the cardboard strips matching the time points. Once all plates were in the box, U.V. lamps were turned on and kept for the appropriate time.
7. The plate was finally removed from the lamp, and the lid was replaced and incubated.
8. In the next lab period, growth was evaluated, and results were placed into a table.
9. Cultures were then disposed into a biohazard bag.

Results

Table 1: Effect of 100◦C temperature

a. Note: (-) no growth; (+) growth

Table 2: Effect of U.V. radiation

a. Note: (-) no growth; (+) growth

Discussion

Bacillus megaterium displayed growth in both elevated temperatures and exposure to Ultraviolet radiation. It survived because of sporulation in this type of bacteria in response to harsh heat conditions, providing dormancy at high temperatures since enzyme proteins change shape as the spore dehydrates. The spores also contain small acid-soluble proteins, which bind, altering DNA conformation, hence photochemistry, providing U.V. radiation resistance.

Enterobacter aerogenes’ survival deteriorates with increased exposure to these two extremes; unlike B. megaterium, it lacks a resistance mechanism for dormancy during harsh conditions. It, therefore, succumbs to increased exposure to both high temperatures and ultraviolet rays. Staphylococcus capitis was also found to be highly susceptible to heat and U.V. radiation. U.V. light caused excitation of oxygen molecules that led to a cytotoxic effect- formation of radicals- which caused cellular death of the bacteria (Shen et al. 6). 100◦C temperatures can also induce apoptosis through lysis of the cell membrane; as is the case with E. aerogenes.

As per the discussion above, the hypotheses concerning S. capitis and B. megaterium are valid. The latter survives by producing endospores that are resistant to the extremities being studied. The former does not prevail since its membrane is susceptible to high temperatures and DNA to the U.V. rays. The hypothesis concerning Enterobacter aerogenes is null since the bacteria failed to survive regardless of being a facultative anaerobe. The extreme heat brought about its failure of survival, above 40◦C optimum temperature, which led to cellular death.

Conclusion

Heat and ultraviolet radiation are two physical methods that can control bacterial growth since they limit their development and functioning. Techniques such as pasteurization and autoclaving are applied where a thermal death point for different microorganisms is aimed. However, bacteriocins that produce endospores such as B. megaterium are harder to sterilize using heat since some spores can survive up to 20 hours in extreme heat. Germicidal lamps are also being applied in laboratories for sterilization since they produce U.V. radiation that mutates bacterial DNA. The mutation is brought about by the formation of thymine dimers formed by exposure of the microbes to U.V. rays.

Work Cited

Shen, Jing et al. “Effect of Ultraviolet Light Irradiation Combined with Riboflavin on Different Bacterial Pathogens from Ocular Surface Infection.” Journal of biophysics, vol. 2017, 2017, pp. 1-7. Hindawi.