Microbiology SC246

Viruses

• What is life? Describe attributes of life that make it distinctive from other parts of the Earth system, such as minerals, water, or light.

• What is life? Describe attributes of life that make it distinctive from other parts of the Earth system, such as minerals, water, or light.

According to Webster:

A state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction.

“life." Merriam-Webster Online Dictionary. 2011. http://www.merriam-webster.com (27 June 2011).

• What is a virus, what qualities do viruses possess that are characteristics of life (from above question), what qualities set them apart from the classic definitions of life?

Life: A state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction.

• What is a virus, what qualities do viruses possess that are characteristics of life (from above question), what qualities set them apart from the classic definitions of life?

Viruses contain DNA or RNA

and a protein coat Some are enclosed by an

envelope Obligate intracellular

parasites Some viruses have spikes Most viruses infect only

specific types of cells in one host

Host range is determined by specific host attachment sites and cellular factors

Viruses

Figure 13.1

• Is a virus a living entity? Why or why not?

• If you define a virus as a living entity, what are the limits of life? Discuss what qualities must be present for something to be considered alive.

• If a virus is not defined as living, what is it? How does it reproduce? How have viruses evolved through time?

Case #1Following a round of water testing in rural Minnesota,

contaminated water was discovered in a stream. The source of the contamination is most likely fecal contamination caused by run-off from a 600-acre dairy farm close to the stream. Heavy rains in the area caused localized flooding and the stream measured water levels well above normal.

After isolating a species of bacteria from the water, the following

laboratory tests were completed. The lab notes are listed under laboratory observations. You should record in the results column a positive or negative for each test. To complete the Gram stain results, simply interpret whether it is Gram positive or Gram negative and list the gram reaction and shape. For example: Gram + rods in singles, Gram negative cocci in chains.

 

1. Interpret the tests in Table 1.1 and answer the questions below:a. What is the result of the Gram stain? b. Does this organism ferment glucose? How can you tell?c. Would the catalase test be helpful to identify your unknown? Why or why not.

2. Using the unknown identification chart, compare the results recorded above. What is the genus and species of the unknown organism? 3. If this water was ingested by humans, what type of infection could result? What types of signs and symptoms would an infected individual display? 4. Is the only source of contamination the dairy farm? Give another possible explanation for the water contamination.

References and photo credits Tortora, G., Funke, B., & Case, C.

(2007). Microbiology: An Introduction (8th ed.). San Francisco, CA: Pearson.