Nutrition Flashcards
Essential elements
CHNOPS Se
Nitrogen
Typical bacterial cell ~12% nitrogen (by dry weight)
Key element in proteins, nucleic acids, and many more cell constituents
Phosphorus (P)
Required by cell for synthesis of nucleic acids and phospholipids
Sulfur (S)
Plays structural role in S-containing amino acids (cysteine and methionine)
Present in several vitamins (e.g. thiamine, biotin, lipoic acid) and coenzyme A
Potassium (K)
Required by enzymes for activity
Magnesium (Mg)
Stabilizes ribosomes, membranes and nucleic acids
Also required for many enzymes
Calcium (Ca)
Helps stabilize cell walls in microbes
Plays key role in heat stability of endospores
Sodium (Na)
Required by some microbes (e.g., marine microbes)
Iron
Plays major role in cellular respiration; key component of cytochromes and FeS proteins involved in electron transport
Under anoxic conditions, generally ferrous (Fe2+) form; soluble
Under oxic conditions: generally ferric (Fe3+) form; exists as insoluble minerals
Cells produce siderophores(iron-binding agents) to obtain iron from insoluble mineral form
Most commonly required growth factors
Most function as coenyzmes
Vitamins
Culture Media
Nutrient solutions used to grow microbes in the laboratory
Defined media:
precise chemical composition is known
Complex media
composed of digests of chemically undefined substances
Contains compounds that selectively inhibit growth of some microbes but not others
Selective media
Contains an indicator, usually a dye, that detects particular chemical reactions occurring during growth
differential media
culture containing only a single kind of microbe
pure
unwanted organisms in a culture
Contaminants
time required for a population of microbial cells to double
generations
Variable among species depending on
Nutritional factors
Genetic factors
Temperature
Most species generation times
hours-days
Under optimal lab conditions
minutes
cell divide after unequal cell growth
Budding
Polar growth
New cell wall material forms from a single point (compared to binary fission where new cell wall material forms throughout the cell)
Large cytoplasmic structures are not partitioned and so
must be formed in the developing bud
biofilm.. benefits?
Planktonic cells attach to a surface
Build a polysaccharide matrix, cells embedded
Resistant to chemicals, antibiotics, abrasion, grazers
Examples of biofilms
Toothbrush
Implanted medical devices
Cystic fibrosis
generation time
of the exponentially growing population is g = t/n
N = No2n can be expressed as
n = 3.3(log N– log N0)
Specific growth rate
(k) (aka instantaneous growth rate constant) rate at which the population is growing at any instant
Instantaneous rate of growth dN/dt=kN
A function of the number of cells at a given time
Reexpress as N=N0ekt
Take log10of both sides N=kt/2.303+log N0
k= 0.301/g(slope of semi-log plot)!!!
since measures a doubling (x2) per generation time and log10of 2 is 0.301
Division rate(v) is calculated as
v= 1/g
Batch culture:
a closed-system microbial culture of fixed volume
Typical growth curve for population of cells grown in a closed system is characterized by four phases
Lag phase
Exponential phase
Stationary phase
Death phase
Lag phase
Interval of time between when a culture is inoculated and when growth begins
Exponential phase
Cells in this phase are typically in the healthiest state
Stationary phase and Death
Net growth rate of population is zero
One divides, one dies = cryptic growth
Either an essential nutrient is used up or waste product of the organism accumulates in the medium
Death phase is exponential
Continuous culture
an open-systemmicrobial culture of fixed volume
most common type of continuous culture device
Chemostat
Both growth rate and population density of culture can be controlled independently and simultaneously by:
Dilution rate: rate at which fresh medium is pumped in and spent medium pumped out
Concentrationof a limiting nutrient
Microbial cells can be enumerated by
microscopic observations; simple but results can be unreliable
Limitations of microscopic counts
Cannot distinguish between live and dead cells without special stains
- Small cells difficult to see and can be overlooked
- Precision is difficult to achieve
- A phase-contrast microscope is required if a stain is not used
Measurement of living, reproducing population is
Viable cell counts (plate counts)
Two main ways to perform plate counts
Spread-plate method
Pour-plate method
To obtain the appropriate colony number, the sample to be counted should always be
diluted
Colony counts should be between ??? (colony-forming units) to be accurate
30 –300 cfu
??? is Typically more accurate than spread plates but counts are usually lower because heat-sensitive cells will not grow after interacting with heated agar
pour-plate
Plate counts can be highly ??
unreliable when used to assess total cell numbers of natural samples (e.g., soil and water)
The Great Plate Anomaly:
Direct microscopic counts of natural samples typically reveal far more organisms than are recoverable on plates of any given culture medium
The Great Plate Anomaly results in
viable but non-cultivable cells (VBNC)
Why viable but non-cultivable cells (VBNC) ?
Microscopic methods count dead cells whereas viable methods do not
Different organisms in even a very small sample may have vastly different requirements for resources and conditions in laboratory culture
? measurements are an indirect but very rapid and useful method of measuring microbial growth
Turbidity; often use spectrophotometer and optical density.
is a major environmental factor controlling microbial growth
Temperature
As temperatures rise, rate of enzymatic reactions
increases and growth rate becomes faster
BUT at a certain temperature, proteins denature and growth slows
the minimum, optimum, and maximum temperatures at which an organism grows
cardinal temperatures
Psychrophile
low temperature
growth is not possible at
min and max temperatures only at optimal
Mesophile
midrange; warm blooded , e coli
thermophile
high temp
hyperthermophile
very high temp
Extremophiles
very hot or very cold
psychrophiles
cod optima; inhabit permanently cold environments
Psychotolerant
Organisms that can grow at 0ºC but have optima of 20ºC to 40ºC; more widely distributed in nature than psychrophiles
What are the molecular adaptation that allow psychrophily
More α-helices, fewer β-sheets
-α-helices provide more flexibility for catalyzing at low temperatures
More polar and fewer hydrophobic amino acids
Fewer weak bonds
Decreased interactions between protein domains
Transport processes function optimally at low temperatures due to modifications of cytoplasmic membranes
High unsaturated fatty acid content
Cytoplasmic membranes remain semi-fluid at low temperatures
Which life form only exists above Above ~65°C
Prokaryotes
Hyperthermophiles in Hot Springs
Chemoorganotrophic (energy from organic chemicals) and chemolithotrophic (energy from inorganic compounds) species present
High prokaryotic diversity (both Archaea and Bacteria represented)
Organisms with the highest temperature optima areArchaea
What are the allowances for Molecular Adaptations to Thermophily
Enzyme and proteins function optimally at high temperatures; features that provide thermal stability:
Critical amino acid substitutions in a few locations provide more heat-tolerant folds
An increased number of ionic bonds between basic and acidic amino acids resist unfolding in the aqueous cytoplasm
Production of solutes (e.g., di-inositol phosphate, diglyercol phosphate) help stabilize proteins
Modifications in cytoplasmic membranes to ensure heat stability
Bacteria have lipids rich in saturated fatty acids
Archaea have lipid monolayer rather than bilayer
Monolayer prevents the cytoplasmic membrane from melting because of covalent links between membrane
What temperature resistant bacteria produce enzymes widely used in industrial microbiology? Example?
Hyperthermophiles
TAQ Polymerae
Other than temperature, what are Other Environmental Factors Affecting Growth
Microbial Growth at Low or High pH
Osmotic Effects on Microbial Growth
Oxygen and Microbial Growth
Toxic Forms of Oxygen
Most organisms grow best between pH 6 and 8
neutrophiles
Acidophiles
organisms that grow best at low pH (< 6)
Some obligate acidophiles; membranes destroyed at neutral pH
Stability of cytoplasmic membrane critical
However, The internal pH of a cell must stay relatively
close to neutral even though the external pH is highly acidic or basic.
Osmotic Effects on Microbial Growth
Typically, the cytoplasm has
a higher solute concentration than the surrounding environment, thus the tendency is for water to move into the cell (positive water balance)
water will flow out unless the cell has a mechanism to prevent this
water will flow out unless the cell has a mechanism to prevent this
Halotoleration
organisms that can tolerate some reduction in water activity of environment but generally grow best in the absence of the added solute
Mechanisms for combating low water activity (unbound water) in surrounding environment involve increasing the internal solute concentration by
water activity scale extends from 0 (bone dry) to 1.0 (pure water)
Pumping inorganic ions from environment into cell
Synthesis or concentration of organic solutes
compatible solutes: compounds used by cell to counteract low water activity in surrounding environment
Often sugars, alcohols, or derived amino acidsSome use KCl
Several toxic forms of oxygen can be formed in the cell – occur during reduction of O2 to water
Single oxygen (O)
Superoxide anion (O2-
)Hydrogen peroxide (H2O2)
Hydroxyl radical (OH.)
Catalase and peroxidase attack H2O
forming O2 and H2
