Chapter 7: Bacterial and Archaeal Growth Flashcards
What’s the process in which most bacteria and archaea reproduce and what are the steps of this process?
Binary fission - reproduction of a cell by division into two approximately equal parts the binary fission of protozoans
- Cell elongation
(enlargement) – cell wall,
plasma membrane, and
volume → increase - Chromosome is
replicated and separated - Cross wall (septum) is
formed, which splits cell
into → two daughter
cells
Bacterial Cell Cycle
• Cell cycle is sequence
of events from the
formation of a new cell
through the → next
cell division
What are the three phases of the cell cycle?
- Growth period after cell
division
• Similar to G1 - Chromosome replicates
and partitions
• Similar to S phase and mitosis - Septum forms and two separate daughter cells are created
• Cytokinesis
Most bacterial have one ____
chromosome
circular
• Single origin of replication – site
at which replication → begins
origin of replication
site at which replication → begins
Terminus
site at which replication is terminated, located
opposite of the origin
Replisome
group of proteins needed for → DNA synthesis
DNA replication proceeds…
In both directions (bidirectionally) from the origin
• Origins move to opposite ends of the cell
There are three parts to the partitioning system:
The ParA, Par B, and ParC.
-ParA and ParB protein act like the eukaryotic →
centromere
-ParS are regions on the chromosome near the origin of replication
ParB then ParA proteins bind onto the ParS sites
• Creates the → partition complex
• ParB and ParA pull the chromosomes by the ParS sites to the opposite poles of the cell
Cytokinesis
occur after cell
division when two daughter
cells are created
Septation
formation of
cross walls between
daughter cells
Cytokinesis
• Selection of site for septum formation
• Assembly of Z ring (composed of protein
FtsZ)
• Assembly of cell wall synthesizing
machinery
• Constriction of cell and septum formation
The Growth Curve
• Observed when microorganisms are grown in → batch
culture
Closed culture with a single → batch of medium
• Usually plotted as logarithm of → cell number vs. time
• Has five distinct phases
Lag phase
time after microbes have been introduced to
fresh medium
• There is no increase in → cell numbers
• During this time cells are either too old or low on ATP and other factors necessary for reproduction
• New factors have to be made to reproduce and cells
need time to recover from their transfer
Exponential (log) phase
microbes are growing and
dividing at the → maximum rate possible
• Based on genetics, the medium used, and
environmental conditions
Stationary phase
common in a closed batch system, cell
population will eventually slows and the growth curve is →horizontal
• Population numbers depend on available nutrients and the type of→ microbe
Possible reasons for stationary phase:
• Nutrient limitation
• Limited oxygen availability
• Toxic waste accumulation
• Critical population density reached
Death phase
the number of viable cells declines because
of cells dying at a constant rate
• Debate as to why this occurs
• Nutrient deprivation or buildup of waste
Viable but nonculturable (VBNC)
cell response to
starving, temporarily unable to grow
• Once conditions improve cells will begin to →grow
again
Programmed cell death
part of the microbial population
is genetically programmed to die after growth stops
• Sacrificing themselves to benefit the population
Long-term stationary phase
(extended stationary phase)–
after a time of death the population → remains constant
• Microbial population evolves to use nutrients that are
available and tolerate → toxins
Generation (doubling) time
Time required for the population to
double in size
• Varies depending on species of
microorganism and environmental
conditions
• Range from 10 minutes for some
bacteria to days for some eukaryotes
Hypotonic solution
(lower osmotic concentration)
• Water enters the cell
• Cell swells and may burst (plasmoptysis)
Hypertonic
(higher osmotic concentration)
• Water leaves the cell
• Membrane shrinks from cell wall (plasmolysis)
• To reduce osmotic concentration of cytoplasm in
hypotonic solutions:
Mechanosensitive (MS) channels in plasma membrane
allow solutes to → leave
To increase their internal osmotic
concentration in hypertonic solutions:
• Increase internal solute
concentration with
(Osmoprotectants) compatible
solutes
• Solutes compatible with metabolism
and growth
Halophiles
require 1.5 % of NaCl or
above
Halotolerant
can grow in high salt
concentrations but do not require it
(up to 10%)
• Staphylococci
Osmotolerant
able to grow in a wide
variety of water or osmotic
concentrations
Extreme halophiles
require salt
concentrations of >10%
Extremely high concentrations of →
potassium
• Cell wall, proteins, and plasma
membrane require high salt to maintain
stability and activity
Halophiles and osmophiles use ___________ to
synthesize or obtain molecules from their environment
compatible solutes
• Keep the osmotic concentration of the cell isotonic to
the cells habitat
• So the plasma membrane is always firmly pressed
against the → cell wall
pH
is the measurement of the acidity of a solution
(hydrogen ion (H+) concentration)
Acidophiles
optimum growth is between pH → 0 to
5.5
• Archaea, fungi, and photosynthetic protists
Neutrophiles
optimum growth is between pH → 5.5-
8.0
• Most bacteria
Alkaliphiles
optimum growth is between pH → 8 to 11.5
• All three domains, wide range, marine microbes
Most microbes maintain an internal pH at
neutral
• Plasma membranes are impermeable to → protons (H+)
• Exchange potassium for protons
Acidic tolerance response when external pH is → too low
• Pump protons out of the cell (ATPase enzyme)
• Some synthesize acid and heat shock proteins that
protect proteins from → denaturation
Many microorganisms change the pH of their habitat by
producing __________
acidic or basic→ waste products
Can microorganisms regulate their internal
temperature?
no
Enzymes have optimal temperature at which they function
optimally
• High temperatures may inhibit enzyme functioning and
be lethal
Organisms exhibit distinct cardinal growth temperatures.
What are cardinal growth temperatures?
• Minimal
• Maximal
• Optimal
Psychrophiles
0C to 20C
Psychrotrophs (phychrotolerant)
0C to 35C
Arctic or Antarctic habitats • Cause spoilage in
refrigerator temperatures
Mesophiles
20C to 45C
• Human pathogens
Thermophiles
45C to 85C
Hyperthermophiles
85C to 100C
• Composts, haystacks, hot
water lines, and hot
springs
Protein structure stabilized by a variety of means
• More hydrogen bonds
• Larger amounts of amino acids (proline)
• Chaperones help stabilize and fold proteins
Histone-like proteins…..
stabilize DNA
Membrane stabilized by variety of means
• More saturated fatty acids, more branched, and higher
molecular weight lipids
• Increases melting points of membrane lipids
Growth in presence of different oxygen concentrations
depends on a microbe’s metabolic processes:
• Electron transport chains (ETC)
• Final electron acceptor is → oxygen
Growth in presence of different oxygen concentrations
depends on a microbe’s metabolic processes:
• Electron transport chains (ETC)
• Final electron acceptor is → oxygen
Obligate aerobes
dependent on oxygen from the
atmosphere (21.5%) for growth
• Most multicellular organisms
Obligate anaerobe
oxygen is toxic, do not need it for
metabolism
Microaerophiles
damaged by atmospheric oxygen (need
2-10% for growth)
Facultative anaerobes
do not require oxygen for
growth…but grow better in its → presence
Aerotolerant anaerobes
grow well with or without oxygen
Oxygen is reduced to….
reactive oxygen species (ROS) –
toxic oxygen products
• Superoxide radical
• Hydrogen peroxide
Aerobes produce protective enzymes that protect them
from ROS
• Superoxide dismutase (SOD)
• Catalase
Strict anaerobic microbes lack or have very low quantities
of →
SOD or catalase
• These microbes cannot → tolerate O2
• Anaerobes must be grown without O2
Microbial environments:
• Are complex and constantly → changing
• Expose a microorganism to overlapping gradients of
nutrients and environmental factors
Microbes have evolved many responses to starvation and
environmental stress:
• Morphological changes (endospore formation)
• Enter stationary phase of growth curve
• Can use cellular components as → nutrients
• Numerous genes and proteins that help
• Viable but not culturable → state
Where do most microbes grow?
Most microbes grow attached to surfaces rather than free
floating
• These attached microbes are members of complex, slime
enclosed communities called a → biofilm
biofilm
complex, slime
enclosed communities
• Biofilms are everywhere in nature
• Can be formed on any conditioned surface
Microbes reversibly attach to conditioned surface and
release polysaccharides, proteins, and DNA to form the
extracellular polymeric substance (EPS)
Additional polymers are produced as microbes ____
and biofilm → ______
reproduce ; matures
The EPS and change in attached organisms’ physiology
protect
microbes from harmful agents
• When formed on medical devices, such as implants,
serious infections can result
• Organism sloughing can contaminate water above biofilm
in a drinking water systems
