Chp. 6 & Chp. 5 selected pages Flashcards
Microbial Growth
- Physical
- Chemical
Physical- temperature, pH, osmotic pressure
Chemical- sources of C, N, S, P, O, trace elements, and organic growth factors
Minimum growth temp
lowest temp at which the species will grow
Optimum growth temp
temp at which the species grows best
maximum growth temp
highest temp at which growth is possible
Psychrophile
-likes 0 to 20 deg C, 15 deg C is optimum
-oceans and polar regions
unlikely to spoil food
e.g.snow algae
Psychotroph
- likes 0-30 deg C, but 20-30 deg C is optimum
- can grow at lower temps
- food spoilage
e.g. molds
Mesophiles
- likes 20-40 deg C
- optimum is 37 deg C
- likes human body temp
- lives in terrestrial and aquatic areas
- on plants and animals
- may cause spoilage
e.g. many bacteria that cause disease are mesophiles
Theromphile
- likes 40-80 deg C, optimum 50-60 deg C
e. g. runoff from hot springs
e. g. Thermus aquaticus in runnoff from hot springs in Yellowstone
Hyperthermophile
- optimum 80 deg C
- many in Archae domain
- inside middle of hot springs
- deep see hydrothermal vents (volcanoes under ocean)
e.g. Sulfolobus, an archaen, lives in YS
pH
A. happiest at neutral
B. acidophile- acids
e.g. molds pH 5, archeans at very low pH in Yellowstone
e.g. Lactobacillus- bacteria in yogurt, lower pH, produces some acids
C. alkaliphile- likes basic environment
To neutralize acids and maintain pH, chemical buffers are included in the growth medium.
Salinity
a. Halophile- likes salty environment, organisms in Mono Lake, Great Salt lake
Osmotic pressure
if in a solution whose concentration of solutes is higher than in cell (environment is hypertonic to the cell), the cellular water passes out through the plasma membrane to the high solute concentration.
Carbon source
- autotroph- uses inorganic source of carbon
- heterotroph- uses organic source of carbon
Chemohetertrophs- get most of their carbon from the source of their energy–organic materials such as proteins, carbohydrates, and lipids.
-Chemoautotrophs and Photoautotrophs derive their carbon from CO2
obligate anaerobe/strict anaerobe-
requires absence of O2 for microbe to survive
microaerophilic
uses small amounts of O2
Oxygen gas and metabolism
- oxygen gas is used by organisms in reactions that yield energy
- oxygen gas can be toxic- various forms of O2 can kill cells
- organisms that use O2 must deal with these toxic forms
obligate anaerobe/strict anaerobe
requires absence of O2 for microbe to survive
aerotolerant
tolerates O2
Biofilms
community of organisms made possible by slime layer (eps)
Extracellular polymeric substance (EPS)
new name for the glycocalyx that helps bacteria attach to surfaces, the old name was slime layer
Biofilms
formed against a surface, such as a rock in a pond, a human tooth, or a mucous membrane
e.g. Streptococcus mutans has a slime layer, causes cavities
Advantages of living in a biofilm
- prevents dehydration
- share nutrients
- protection from host immune system
- antibodies (proteins produced by host that fight infection)
- phagocytosis by WBC
- protection from antibiotics used in the treatment of disease
Biofilms and Human health
- biofilms form on almost all medical devices
- encountered in many disease conditions, such as infections related to the use of contact lenses, dental caries, and infections by pseudomonad bacteria.
Bacterial method of reproduction
Bacteria normally reproduce by Binary Fission
- cell elongates and DNA is replicated
- CW and PM begin to restrict
- Cross-wall forms, complete separating the two DNA copies
- Cells separate
a. direct microscopic count
b. indirect count
a. get an exact cell number
b. not necessary to count microbial cells to estimate numbers
standard plate count
a. serial dilutions- dilutions to do in a row
b. grow bacteria on media in petri plates- 1 ml in plates
c. count colonies and calculate cfu/ml
turbidity
a. use spectrophotometer
b. measure light absorbance of test tube with bacteria
c. measurements are in O.D. (optical density)
- can correlate with standard plate count
Dry weight
a. bacteria removed from growth medium
b. filter to remove extraneous material
c. dried in desiccator
Growth curve
- lag phase
- exponential phase
- stationary phase
- death phase
lag phase
organisms get used to the medium
exponential phase
optimal growth, rapid cell division
stationary phase
nutrients start to run out, some cells die, some still growing, stagnant
death phase
cell death
Generation time/doubling time
time it takes for 1 cell to divide into 2
N= N0 2^n
N0= number of cells at the beginning
N is total number at the end
n is number of generations
Nitrogen cycle
nitrogen in the atmosphere goes through fixation, nitrification, and denitrification. Nitrates assimilated into plants and animals after nitrification go through decomposition, ammonification, and then nitrification again.
Ammonification
release of ammonia
Nitrogen Nitrification
The next sequence of reactions in the nitrogen cycle involves
the oxidation of the nitrogen in the ammonium ion to produce
nitrate
Nitrogen Denitrification
can lead to a loss of nitrogen
to the atmosphere, especially as nitrogen gas
Nitrogen fixation
bacteria, such as cyanobacteria, directly uses as a nitrogen source and convert nitrogen gas to ammonia
Nitrogen-fixing bacteria
Rhizosphere
Azotobacter
Clostridium
Photosynthesis
first step of carbon cycle in which photoautotrophs such as cyanobactera, green plants, algae, FIX carbon dioxide into organic matter using energy from sunlight
Carbon cycle second step
chemoheterotrophs such as animals and protozoa, eat autotrophs and in turn be eaten by other animals
- thus, organic compounds of the autotrophs are digested and resynthesized, the carbon atoms of CO2 are transferred from organism to organism up the food chain
- when chemoheterotrophs satisfy energy requirements, energy released through respiration, CO2 immediately becomes available to restart cycle.
Decomposer
When plants and animals die, organic compounds are decomposed by bacteria and fungi
