MB 351 - Lecture 14 & 15 (Requirements for growth) Flashcards
Obligate Aerobe
require O2 as final e- acceptor in aerobic respiration. air is 21% Ox
Obligate anaerobes (aerophobes)
do not need O2. O2 is toxic, and can kill or inhibit growth. Live by fermentation, anaerobic respiration, bacterial photosynthesis. (Marshes, deep subsurfaces)
Facultative anaerobes
can switch between aerobic and anaerobic types of metabolism
Microaerophile
requires oxygen to survive, but requires environments containing lower levels of oxygen than are present in the atmosphere
Aerotolerant anaerobe
Don’t use O2 for growth, but tolerate it. Exclusively anaerobic metabolism.
The medium that may be used to grow microorganisms under aerobic conditions, or to test for the oxygen requirements of a bacterium.
Thioglycollate - medium that serves as a reducing agent to remove traces of O2 by reducing it to water. Pink dye when oxidized and colorless when reduced
Toxic oxygen: Normal molecular O2 that has been boosted into a higher energy state and is extremely reactive
Singlet Oxygen
Toxic oxygen: Formed in small amounts during normal respiration of microbes that use oxygen as the final e- acceptor. These radicals are toxic to cellular components. Toxicity is caused by their great instability, which leads them to steal an electron from a neighboring molecule, and this repeats itself.
Superoxide free radicals or superoxide anions
Toxic oxygen: Peroxide anions
Produced as part of Hydrogen peroxide
Toxic oxygen: Formed in the cytoplasm by ionizing radiation. Most reactive intermediate form of oxygen.
Hydroxyl radical (OH.)
Toxic oxygen: Cells contain several enzymes that aid when exposed to the peroxidation of lipids:
superoxide dismutase, catalase, peroxidase, as well as cellular antioxidants which are able to scavenge oxygen free radicals and repair peroxidized lipids. Able to convert theses toxic oxygen radicals to something less damaging, like water.
Chemical Requirements for growth: macromolecules
Elements: CHNOPS Mineral ions: K+, calcium, sodium, magnesium, iron (Fe2+, Fe 3+), chlorine -mineral ions play an important role in enzymes and macromolecules
Sources of Carbon: Heterotrophs
Rely on other organisms to form the organic compounds (such as glucose, proteins, lipids) that they use as carbon sources. -Carbon source also typically supplies H and O -Carbon source supplies energy (glucose)
Sources of Carbon: Autotrophs
-Use inorganic CO2 as sole or principal carbon source -Carbon source does not supply energy -CO2 fixation
Autotroph: Chemoauto(litho)trophs
inorganic chemicals as energy (ammonia, nitrite, iron, hydrogen sulfide, hydrogen).
Autotroph: Phototrophs
light as an energy source
Sources of N
required as proteins and nucleic acids. Acquired from Amino acids, NH4+, NO3-, also N2- fixation (cyanobacteria)
Sources of S
required for S-amino acids (cysteine and methionine), vitamins Acquired from inorganic sulfate (SO4^2-)
Sources of P
required in nucleic acids, phospholipids, ATP, proteins. Acquired from PO4^2-
Micronutrients
Trace Elements and Growth Factors
Trace Elements
-Inorganic transition metals (Mn, Fe, Mo, Cu, B, Co). -typically required in microgram quantities -serve structural/catalytic roles in specific enzymes -Key trace element: Fe for cellular respiration (redox center), or functions as cofactors in enzymes involved in e- transport rxns
Growth Factors
-Small organic compounds: amino acids, purines/pyrimidines, vitamins (enzyme cofactors) -required in varying concentrations -some organisms satisfy their own requirements for growth factors
Physical requirements for growth:
Temperature, pH, and water availability
Effects of temperature on growth: temperature affects microbes in two opposing ways
As temperature rises, the rate of enzymatic rxns increases, and growth becomes faster. However, above certain temperatures, proteins may become denatured or damaged.
Minimum temperature
Below this temperature, growth is not possible. Below this temperature membrane gelling; transport processes so slow that growth cannot occur
Optimum Temperature
Enzymatic reactions occurring at maximal possible rate
Maximum temperature
Above which growth is not possible. Above this temperature, proteins denature. Collapse of the cytoplasmic membrane; thermal lysis.
Cardinal temperatures
Min, optimum, and max temperatures. These characteristics vary dramatically between species
cold loving microbes
psychrophiles - low temperature optima O deg C to 11 deg C
moderate-temperature loving microbes
mesophiles - midrange temperature optima 9 to 48degC E.Coli
High temperature optima
thermophiles - live and grow at temperatures that exceed 50degC
Very high temperature optima
hyperthermophiles - exceeding 85-90degC
pH requirements: 3 types of bacteria
neutrophils, acidophiles, alkaliphiles
neutrophils
grow best in neutral environments pH >5.5 and
acidophiles
grow best in acidic conditions pH
alkaliphiles
prefer basic conditions pH of 8 or above. found in highly alkaline habitats such as soda lakes and high carbonate soils
Osmotic Pressure
is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. High osmotic pressures have the effect of removing necessary water from a cell.
Water availability is not only influenced by moist vs. dry conditions but also on the ____________
concentration of solutes
Osmotic pressure: Normal cell conditions
isotonic solution: the solute concentration in the solution and in the cell
When a microbe is in a solution whose concentration of solutes is higher than in the cell, the environment is __________ to the cell
Hypertonic. This causes the cellular water to pass out through the plasma membrane to the high solute concentration.
The osmotic loss of water causes ________ or _______ of the cells cytoplasm. This inhibits cell growth.
plasmolysis, or shrinkage -uses to preserve food
Halophiles
-organisms that can live/thrive in high salt concentrations -Seawater contains 3% NaCl, microbes that inhabit these marine environments almost always have a NaCl requirement for growth
Capable of growth in very salty environments
extreme halophiles (15-30% NaCl for optimum growth)
Microbes that can tolerate some level of dissolved solutes, but grow best in the absence of added solute or very limiting quantities
Halotolerant
Do not require high NaCl concentrations, but are able to grow at salt concentrations up to 2%, a concentration that inhibits the growth of many other organisms
facultative halophiles
requires oxygen to survive, but requires environments containing lower levels of oxygen than are present in the atmosphere
Microaerophile
Don’t use O2 for growth, but tolerate it. Exclusively anaerobic metabolism.
Aerotolerant anaerobe
Min, optimum, and max temperatures. These characteristics vary dramatically between species
Cardinal temperatures
Produced as part of Hydrogen peroxide
Toxic oxygen: Peroxide anions
