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
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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
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Osmotic Concentration
Different reactions according to environment.
Hypotonic
Hypertonic
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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
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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+
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Extreme acidophiles
Import cations (ex. K+) to decrease uptake of H+
Proton pumps
Impermeable cell membranes
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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
