Download MICROBIAL GROWTH

MICROBIAL GROWTH
Chapter 6
About GROWTH.........
• Usually means an increase in size however…..
• Microbes grow by increasing in number and not in size
• They can accumulate into clumps of hundreds and colonies of
thousands
• COLONIES = large number of microbes usually derived from
one organism (clone)
• Unicellular organisms do grow in size but ONLY until the
mother cell doubles in size and duplicates its contents
• The mother cell divides into 2 new daughter cells
• This process is called binary fission
GROWTH REQUIREMENTS
–
•
•
Obligate vs facultative:
–
–
Obligate: must have the specific environment
Facultative: able to adjust to fluctuations or a range of environmental
factors
PHYSICAL REQUIREMENTS
–
–
–
pH
TEMPERATURE
OSMOTIC PRESSURE
–
–
–
C and N sources
H2O and Oxygen requirements
Organic growth factors & trace minerals
BIOCHEMICAL REQUIREMENTS
1. pH
• BUFFERS: stabilizes pH of a solution
– Able to take up or donate H+ to the solution
• OPTIMUM for most bacteria = pH 6.0-8.0
– Best if between 7.2 – 7.6
• Normal human physiological pH
• Neutrophiles
• ACIDOPHILES - can grow at low pH
– Lower than pH 4.0
• ALKALIPHILES - can grow at high pH
• OPTIMUM for yeast = pH 4.0 - 5.0
2. TEMPERATURE
•
•
•
•
Temperature range
–
Minimum, OPTIMUM, Maximum
–
Optimum: 15 - 30 C
–
Optimum: 28-45 C
–
–
Optimum: 55-75 C
Extreme thermophiles: 65-110 C
Psychrophiles: cold loving 0-35 C
Mesophiles: moderate temp. loving  10-47 C
Thermophiles: heat loving  40-80 C
3. OSMOTIC PRESSURE
• Force with which a solvent moves from a solution of lower
solute concentration to solution of higher solute concentration
• HYPERTONIC solution: conc. of solutes outside > inside
– Plasmolysis occurs
– Preserve foods
• HYPOTONIC solution: conc. of solutes inside > outside
• HALOPHILE - salt loving
– Extreme halophile (30% NaCl) - Archaea
– Facultative halophile (2 % NaCl)
BIOCHEMICAL REQUIREMENTS
• Each organism has it’s own range of nutritional requirements in
addition to its physical needs
• Can be classified based on carbon source
• Can be classified based on amount of oxygen needed
• Each organism differs in it’s requirements for nitrogen, sulfur
and phosphorous sources or requirements for other trace
elements
CARBON SOURCE
• Carbon = structural backbone of all living matter
• Chemoheterotrophs:
– C and energy derived from organic compounds like proteins,
carbohydrates and lipids
• Chemo- & photoautotrophs: C from CO2
– Chemoautotrophs get their energy from inorganic compounds
– Photoautotrophs get their energy from sunlight
NITROGEN
• USES
– Amino acids/proteins
– Nucleic acids: DNA, RNA
– ATP
• SOURCES
– Breakdown of protein containing materials
– Ammonium ions (NH4+) and nitrate ions (NO3-)
• NITROGEN FIXATION:
– Process where an organism is able to N from gaseous N2
– Cyanobacter
– Rhizobium: Symbiotic relationship with plants
SULFUR
• USES
– Amino acids: Cysteine, Methionine
– Vitamins: Thiamine, Biotin
• SOURCES
– Sulfur containing compounds such as S-containing amino acids and
inorganic sulfate salts & some vitamins
– SO4 2– H 2S
PHOSPHOROUS
• USES
– Nucleic acids: DNA, RNA
– ATP
– Phospholipids
• SOURCES
– PO4
3-
Trace Elements & Organic Growth Factors
• ESSENTIAL = can not synthesize therefore MUST BE
SUPPLIED
• TRACE ELEMENTS
•
•
•
•
– Essential cofactors/coenzymes
– K, Fe, Cu, Mb, Zn
Vitamins
Amino acids
Purines
Pyrimidines
OXYGEN
-
• USEFUL: respiration final e acceptor
• HARMFUL: strong oxidizer
• OBLIGATE AEROBES - require O2 to live
– Use O2 as final electron acceptor
– Contain enzymes that detoxify excess molecular oxygen
• FACULTATIVE AEROBES - can use but does not require O2
• OBLIGATE ANAEROBE - unable to use O2
– Lack detoxifying enzymes
• AEROTOLOERANT ANAEROBE - does not use O2 but can grow in it’s
presence (1 – 2% O2)
• MICROAEROPHILE - requires less O2
– Needs 5-10% CO2 to initiate growth
O2 : Good or Bad?
• Reactive and Toxic byproducts
–
–
–
–
–
Highly unstable allowing them to steal electrons from nearby molecules
Singlet Oxygen
Superoxide free radical (O2.-)
Peroxide (O2-2)
Hydroxyl
• Detoxifying enzymes
– SOD: Superoxide dismutase
.+
• Converts 2 O2 + 2H  O2 + H2O2
– Catalase
• Converts H2O2  O2 + 2 H2O
– Peroxidase
• Converts H2O2 + 2H+  2 H2O
BACTERIAL GROWTH & DIVISION
•
•
GROWTH = orderly process of the increase in the number of
individual microbes
–
–
–
There is an increase in size followed by cell division
BINARY FISSION - most bacteria divide in this manner
Some yeast replicate by budding – new cell is smaller than mother cell
–
–
–
–
Elongation of cell and DNA duplication
Cell wall & plasma membrane increase and start folding inward
Formation of cross wall between DNA regions
Cells separate into 2 new identical cells
DIVISION = 4 steps for 1 cell to divide into 2 cells
GENERATION or DOUBLING TIME
• Length of time required for a generation of cells to divide
(double)
• Length of time will vary:
– Depends on particular organism
– Depends upon environmental factors
– Minutes to hours (usually less than 1 hour)
• Because they double in number at every division it is difficult
to plot cell numbers using arithmetic numbers
– Usually use a logarithmic scale to graph bacterial growth
Bacterial Growth Curve
•
Four phases for bacterial growth if an old culture  fresh
medium
• LAG
–
–
–
Increase in cell size and division
Intense increased metabolic activity
Sensitive to physical & chemical damage
• LOG/EXPONENTIAL
–
–
–
•
•
Maximal growth and cell division
• Cells doubling at the fastest rate
• Cell size is slightly decreased
Increased metabolic activity
Sensitive to physical & chemical damage
Bacterial Growth Curve (cont)
STATIONARY
–
–
–
–
Growth rate eventually decreases then stops
# of new cells = # of dead cells
Nutrient depletion
Metabolic byproducts
–
Whole culture dies at first slowly then exponentially
DEATH (DECLINE)
MATH: Arithmetic vs Logarithmic
• PLOT: Cell # vs Generations
• CALCULATIONS: Mf = (Mi) 2n
M f= final number of bacteria
M i= initial number of bacteria
– n = number of generations
• If know any 2 of the 3 above numbers we can solve