Lecture 9: Microbial Growth and Control (Ch7,8,and 9) Flashcards
The reproductive strategies of eukaryotic microbes
– Asexual and sexual, haploid and diploid
Reproductive strategies of bacteria and Archaea
- Haploid only, asexual- binary fission, budding, filamentous - All must replicate and segregate the genome prior to division
most bacteria divide by
binary fission
what are the two pathways that cycle during binary fission
- DNA replication and partition - Cytokinesis
Reproduction in prokaryotes
- Binary fission - Budding - Conidiospores (actinomycetes) - Fragmentation of filaments
What is generation time
(doubling time) is the time it takes for a population to double
A population of microbes that doubles at a constant rate is an example of
exponential growth
What are the 4 phases of the growth curve
- Lag phase - Exponential (log) phase - Stationary phase - Death phase
What occurs during the lag phase of the growth curve
- Cell synthesizing new components
What occurs during the exponential phase of the growth curve
- growth and division is constant and maximal - population is most uniform in terms of chemical and physical properties during this phase
What occurs during the stationary phase of the growth curve
- closed system population growth eventually ceases, total number of viable cells remains constant. (active cells stop reproducing or reproductive rate is balanced by death rate)
Generation (doubling) time varies depending on
species of microorganism and environmental conditions
The range of generation (doubling) time is from ____ minutes for some bacteria to _______ for some eukaryotic microorganisms
10 minutes for some bacteria to several days for some eukaryotic microorganisms
Direct methods for measuring microbial growth
- Plate counts - Filtration - MPN (most probable number) - Direct microscopic count
What are the indirect methods for measuring microbial growth
- Turbidity - Metabolic activity - Dry weight
how to perform viable counting with spread and pour plate techniques
- Spread and pour plate techniques (the difference is one you spread out and the other you add melted nutrient agar and swirl to mix) ( note that in the spread they only grow on the surface and in the pour method they go on and in the medium) (the pour plate method is used with anaerobes because they can grow under the agar) - Diluted sample of bacteria is spread over solid agar surface or mixed with agar and poured into Petri plate - After incubation the number of organisms are determined by counting the number of colonies multiplied by the dilution factor - Results expressed as colony forming units (CFU)
viable counting via the membrane filter technique
- bacteria form aquatic samples are trapped on membranes - membrane soaked in culture media - colonies grow on membrane - colony count determines number of bacteria in sample
If a microbe cannot be cultured on plate media then
dilutions are made and added to suitable media (turbidity determined to yield the most probable number (MPN))
bacterial growth can be measured with a _____, which measures the absorbance at 600nm
spectrophotome
Do bacteria have limited control over their internal environments
Yes. This is why the environmental factors affect microbial growth
Requirements for growth can be divided among ___ and ____ requirements
Physical and chemical requirements
What are some physical requirements that regulate bacterial growth
- Temperature - pH - Osmotic pressure
What some of the chemical requirements that regulate bacterial growth
- Carbon - nitrogen, sulfur, phosphorous - Trace elements - Oxygen - Organic growth factor
Examples of osmotolerant microorganisms
- Staphylococcus aureus - Saccharomyces rouxii
Examples of Halophile (requires high levels of sodium chloried, usually above about 0.2M, to grow)
- Halobacterium, Dunaliella, Ectothirohodospira
examples of Acidophile (Growth optimum between pH 0 and 5.5)
- Sulfolobus - Picrophilus - Ferroplasma - Acontium
Temperature range of psychrophiles
0- 20 degrees C
temperature range of psychrotrophs
0-35 degrees C
Temperature range of mesophiles
20-45 degrees C
Temperature range of thermophiles
55-85 degrees C
Temperature range of hyperthermophiles
85- 113 degrees C
Danger zone for bacterial growth
- 15-50 degrees C - 60-130 degrees F
What are the cardinal temperatures
Minimum, maximum, and optimum temperature
Adaptations of thermophiles
- Protein structure stabilized by a variety of means: more H bonds, more proline, and chaperones - Histones- like proteins stabilize DNA - Membrane stabilized by variety of means (more saturated, more branched and higher molecular weight lipids, ether linkages (archaea like membranes)
Most bacteria grow between pH ____ and ____
6.5 and 7.5
Molds and yeasts how between pH ___ and ___
5 and 6
______ grow in acidic environments
Acidophiles
What is the optimum pH for acidophilus
pH 0 and pH 5.5
Neutrophils growth is optimum between pH ____ and _____
pH- 5.5 and pH 7
Alkaliphiles (alkalophiles) growth optimum is between
pH 8.5 and pH 11.5
Toxicity is a measure of ______
Osmotic pressure (hypertonic, isotonic, hypotonic)
Hypertonic environments, or an increase in salt or sugar, cause _____
Plasmolysis
Halophiles grow optimally at
NaCl concentration greater than 0.2 M
Extreme Halophiles require NaCl concentration
Greater than 2 M
Chemoheterotrophs use ______ carbon sources
Organic
Autotrophs use _____ carbon sources
CO2
Osmotolerant
Able to grow over wide ranges of water activity or osmotic concentration
Halophile
Requires high levels of sodium chloride, usually above about 0.2 M, to grow
Obligate aerobe
Completely dependent at atmospheric O2 for growth
Facultative anaerobe
Does not require O2 for growth but grows better in its presence
Facultative anaerobe
Does not require O2 for growth but grows better in its presence
Aerotolerant anaerobe
Grows equally well in presence or absence of O2