CH 7 microbial growth Flashcards
CH 7
Microbial growth
Speaking in terms of an increase in the number of viable cells in the culture due to:
- binary fission
- budding
- fragmentation
- spores
CH 7
Microbial division
Via mitosis process and cytokenesis
CH 7
Chromosome Replication
Circular structure of DNA affects the replication process: longest process in dividing, works same for plasmids
Origin of replication
Replicates in both directions (unique to prokaryotes) until it reaches the terminus (stops DNA replication)
Multiple rounds of DNA replication occurring at the same time
CH 7
Origin of Replication
Specific DNA sequence
Organize the replication machinery (replisome) - bacterial replication (circular chromosome)
CH 7
Chromosome Partitioning
Segregation of newly replicated chromosomes to opposite ends of the cell
- regulated by cytoskeleton
- MreB (actin filiments separate the chromosome)
CH 7
E. coli and multiple replications
E. coli can divide every 20 minutes, but it takes 40 minutes for their chromosome to be replicated. This is an example of multiple rounds of DNA replication occurring at the same time.
CH 7
Theta replication
Intermediary structure in bacterial circular DNA replication - bidirectional replication from one origin of replication and two replication forks creates a “theta” structure.
CH 7
Plasmid replication
Origin of replication is different from bacterial chromosomes - they determine how often plasmids replicate
CH 7
Cytokenesis
Cell division occurs by septation, the forming of a septum (division, cross wall) between two daughter cells.
Regulated by FtsZ, which pulls the plasma membrane in to help pinch the cell in two.
- assembly of Z ring in the center of the cell
- linkage of the Z ring to plasma membrane
- assembly of cell wall synthesizing machinery
- constriction of Z ring and septum formation to divide cell
CH 7
Forming a new cell wall
Elongation of cell and formation of new peptidoglycan - determines shape of cell
Autolysins break down the existing wall. With no wall preventing it, water comes in and increases the turgor pressure, causing the cell to swell. Autolysins only destroy certain parts of the cell wall - two methods: division and elongation.
CH 7
Division
Autolysins destroy peptidoglycan in a 3D band around the middle of the cell where it will divide - cell expands in that area.
CH 7
Elongation
via turgor pressure–swelling from water uptake when original wall broken down in parts
CH 7
Environmental Factors in microbial growth
Osmotic concentration pH Temperature Oxygen concentration Barometric pressure Radiation
CH 7
Optimal growth conditions
Each microorganism has optimal conditions for growth
- often tolerate a wide range of environmental conditions
Extremophiles
- grow under severe environmental conditions
CH 7
Osmotic Concentration
Different reactions according to environment.
Hypotonic
Hypertonic
CH 7
Osmotic concentration in hypotonic environment
Cell wall limits water entering the cell, and inclusion bodies limit water coming in along the gradient by taking macromolecules out of solution.
Contractile vacuoles
Mechanosensitive channels - aquaporins that allow water to enter, but when the cell swells the channels in the plasma membrane undergo a conformational change and water can’t pass through.
CH 7
Osmotic concentrations in hyptertonic environments
Water flows out of the cell causing plasmolysis. To avoid this, cells increase osmotic concentration of cytoplasm by accumulation of compatible solutes.
- amino acids, potassium, sucrose, polyols
CH 7
Water activity
a w - measure of water availability
Xerophiles grow at very low water activity levels
Osmotolerant microbes grow over a wide range of water activity
Halophiles grow optimally at high salt concentrations (0.2M - 6M)
Saccharophiles grow at high sugar concentrations
CH 7
pH effects on microbial growth
Acidophiles to extreme alkalophiles
They’ll condition their environment to meet their pH requirements; also limiting other types of organisms that can’t survive those conditions - less competition.
Even with extreme organisms, their internal pH is maintained around neutral (range of 6-8 pH). Have to maintain pH difference:
- internal buffering
- proton pumps (ex. ATP synthase)
- acid shock proteins prevent denaturation
some can secrete acids/bases to condition the environment
CH 7
Groupings of bacteria based on favored pH
Acidophiles - 0-5.5 Neutrophiles - 5.5-8 Alkalophiles - 8-11.5 Extreme alkalophiles - 10+
CH 7
Extreme acidophiles
Import cations (ex. K+) to decrease uptake of H+
Proton pumps
Impermeable cell membranes
CH 7
Extreme alkalophiles
Exchange internal Na+ for external H+
CH 7
Temperature effects on microbial growth
Cardinal temperatures: min max optimum Types of bacteria based on preferred temps - psychrophiles - psychotrophs - mesophiles - thermophiles - hypothermaphiles
CH 7
Psychrophiles
0-10C
Arctic, antarctic, oceans
CH 7
Psychotrophs
facultative psychrophiles
20-30 C
refrigerated food spoilage
CH 7
Mesophiles
20-45 C
Human pathogens
CH 7
Thermophiles
55-65 C
composts, hot springs
CH 7
Hyperthermophiles
85-113 C
deep sea vents
CH 7
Adaptive features for extreme temps
Changes in cell membranes
Goal is to stabilize proteins
- different types of enzymes (different form, probably more disulphide bonds)
- chaperone (heat shock) proteins help maintain shape and functionality
CH 7
Oxygen requirements
Classifications:
- oblicage aerobes
- microaerophiles
- facultative anaerobes
- aerotolerant anaerobes
- obligate anaerobes
CH 7
Obligate aerobes
Require oxygen for growth
CH 7
Microaerophiles
require low levels of oxygen for growth
CH 7
Facultative anaerobes
Do not require oxygen but grow better in its presence
aerobic respiration v. fermentation
CH 7
Aerotolerant anaerobes
do not use oxygen but can grow in its presence
CH 7
Obligate anaerobes
Cannot grow in presence of oxygen
require special handling in laboratory
CH 7
Fluid Thiolycolate
Reducing agent that gets rid of oxygen in media. Oxygen gradient in media starts at the top - inoculate the tube, but bacteria will only grow at the proper oxygen gradient - helps ID the type of oxygen environment these bacteria need to survive.
CH 7
Toxic forms of reactive oxygen species
Superoxide radical O2•, hydroxyl radical OH•, and hydrogen peroxide (H 2 O 2 )
These interact with any and all molecules and can cause damage by accepting or donating electrons. Aerobic species have enzymes to deal with these oxygen particles, by obligate anaerobic species cannot grow in oxygen because the radicals cause them to accumulate mutations and they die.
CH 7
Enzymes for dealing with reactive oxygen species
Superoxide dismutase
catalase
peroxidase
CH 7
Catalase test
When catalase is converting hydrogen peroxide to H+ and H 2 O, it bubbles. If not, that means the H 2 O 2 is killing the bacteria.
CH 7
Pressure
An unusual requirement, usually pertains to deep ocean species.
Barotolerant: can survive and grow under high pressure (600-1100 atm)
Barophilic: grow more rapidly under high pressure; may require high pressure for growth. Difficult to grow in the lab.
CH 7
Radiation
Detriment to most microbial growth.
Ionizing radiation (X-rays and gamma)–use on food
- gamma is used to sterilize materials, even food
- Bacteria form resistant endospores
UV light— produces thymine dimers in DNA - mutation that eventually kills bacteria–set things in sunlight to kill microbes
Visible light— reactive oxygen (photooxidation)
- cartenoid allows microorganisms to survive sunlight
CH 7
Deinococcus radiodurans
Can survive a dose of 3-5 million rads (lethal dose for humans is 100 rads)
Possibility of life in space/ other planets
CH 7
Photooxidation
When visible light creates free radicals of singlet oxygen. Vitamin E and carotenoids can repair this.
