University of Houston

MICRO 3332

Quiz 3

1)Which statement below is false?

1. 1. Analysis of DNA content would not be a direct measure to measure microbial growth
   2. The best method for determining viable cell numbers in a sample is to dilute the sample, plate samples, and count colonies on the plates
   3. Pure culture work to obtain isolated colonies is best done using liquid media
   4. Petroff-Hauser counting chamber: direct measurement of cell counts
   5. 0.1 mL of a culture sample diluted to 1/10^3 was plated on media and yielded 40 colony forming units; the sample contains 4x10^5 cfu/mL
2. Bacterium X has a generation time of 25 minutes. Starting with 20 cells in log phase, how long does it take to produce about 100,000 cells?
   1. About 24 hours
   2. About 307 minutes
   3. About 5000 minutes
   4. About 150 minutes
3. Two cells of the bacterium Rhodococcus rhodochrous colonize the soil; after 4 days there are 100,000 bacteria. What is the doubling time of this bacterium?
   1. 5760 minutes or 96 hours
   2. About 937 minutes or 15.6 hours
   3. About 282 minutes or 4.7 hours
   4. About 369 minutes or 6.1 hours
   5. >10 hours
4. Among the choices A-E, which of the following is the best definition of generation time?
   1. The length of time needed for lag phase
   2. The length of time needed for a cell to divide
   3. The lowest rate at which a population doubles
   4. The duration of log phase
   5. The time needed for DNA replication
5. Growth in fed-batch culture is best represented by which growth plot?

1. 1. 

      

      a

1. 2. 

      b

1. 3. c

5. 4. d
6. Correctly match the following
   1. Engulfment by the mother cell and deposition of dipicolinic acid highlight this process:
   2. Persistent nutrition addition allow the cells to maintain a constant level of growth indefinitely
   3. Cellular communication & exopolysaccharide production characterize this
   4. When severely stressed, these bacteria produce highly resistant dormant forms

7. The characteristics listed in i-iii below would likely apply to which state of batch cell growth?

1. Decrease in cell size in this period
2. If a species were an endospore former, it would be occurring here
3. Susceptibility to penicillin would be very low during this time
   1. Death phase
   2. Stationery phase
   3. Lag phase
   4. Mid-log phase

8. The constituents shown comprise a bacterial growth medium. Based on the composition of this medium you can be certain that:

8. 1. It is a complex medium capable of growing heterotrophs
   2. Chemoorganotrophs could grow on this medium
   3. It is a defined medium that would support growth of chemoautotrophs
   4. Chemolithotrophs could grow on this medium
   5. Two of the above are correct
9. Lack of an essential nutrient in a growth medium would likely yield which growth pattern?

1. 1. A
   2. B
   3. C
   4. D
   5. Neither A, B, C, or D; no growth would occur at all