Classify microbes into five groups on the basis of preferred temperature change
Psychrophiles- -10-20 degrees C
Psychrotrophs- 0-20/30 degrees C
Mesophiles- 10-50 degrees C
Thermophiles- 40-70 degrees C
Hyperthermophiles- 65-110 degrees C
importance of osmotic pressure to microbial growth
Osmotic pressure needs to be just right so that there is the needed amount of water in the cell for growth. Most microorganisms must be grown in a medium that is nearly all water- agar is usually at 1.5% so as to not inhibit the growth of bacteria.
use for each of the four elements (C, N, S, P) needed in large amounts for microbial growth
1)Carbon-Structural organic molecules, energy source
2) Nitrogen- In amino acids and proteins, most bacteria decompose proteins
3) Sulfur- In amino acids, thiamine, and biotin. Most bacteria decompose proteins
4) Phosphorus- In DNA, RNA, ATP, and membrane
how microbes are classified on the basis of oxygen requirements
1) Obligate aerobes- Oxygen required
2) Facultative anaerobes- better growth with oxygen. I.e. e. coli
3) Obligate anaerobes- no oxygen
4) Aerotolerant anaerobes- prefers oxygen, as long as its in a lower concentration than the air
Microaerophiles- aerobi
ways in which aerobes avoid by toxic forms of oxygen
Peroxide anion: 2H2O2 catalase ----> 2H2O + O2
catalase breaks down oxygen
bacterial colony
a visible group of bacteria growing on a solid medium, presumably arising from a single microorganism
how pure cultures can be isolated by using streak plates
A sterile inoculating loop is dipped into the mixed culture that contains more than one type of microbe and is streaked in a pattern over the surface of the nutrient medium. As the pattern is traced, bacteria are rubbed off the loop onto the medium. The l
bacterial growth, including binary fission
Binary fission- one cell gives 2 cells that are identical.
Budding- form a bud that enlarges until it grows as big as the parent cell, and then it separates. There is also fragmentation of filaments, and producing chains of conidospores carried externally
Compare the phases of microbial growth and describe their relation to generation time.
1) lag phase- inoculate bacteria in broth, no reproduction
2) log phase- log or exponential growth of bacteria
3) stationary phase- period of equilibrium, bacterial death due to lack of food is equal to the number of new bacterial growth
4) death phase- m
Explain four different methods of measuring cell growth
1) Serial dilutions and plate counts- Can count numbers of colonies, amount of bacteria in 1mL of dilution
2) Filtration- Filter in cup, vacuum pulls bacteria in medium. Have nutrient broth and then grow colonies and count colonies.
3) Direct microscopic
Differentiate between direct and indirect methods of measuring cell growth
Direct- measurement of the growth of microbial populations through measuring cell numbers, measuring the population's total mass (direct counts on small samples).
Indirect- Not always necessary to count microbial cells to estimate their numbers
Explain three indirect methods of measuring cell growth.
1) Turbidity- As bacteria multiply in a liquid medium, the medium becomes turbid, or cloudy with cells. Use a spectrophotometer- a beam of light is transmitted through a bacterial suspension to a light-sensitive detector. As bacterial numbers increase, le
calculations on bacterial growth, generation time
generation time= 60 minutes X hours/ number of generations.
Number of generations= log #cells(end)- log #cells(beginning)/.301 (log10 of 2)
Generation time
Escherichia coli- 20 minutes
Staphylococcus aureus- 30 minutes
Mycobacterium tuberculosis- 16 hours