Chapter 7: Bacterial and Archaeal Growth Flashcards by Christina Lulgjuraj

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

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Bacterial Cell Cycle

• Cell cycle is sequence
of events from the
formation of a new cell
through the → next
cell division

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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

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Most bacterial have one ____
chromosome

circular

• Single origin of replication – site
at which replication → begins

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origin of replication

site at which replication → begins

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Terminus

site at which replication is terminated, located
opposite of the origin

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Replisome

group of proteins needed for → DNA synthesis

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DNA replication proceeds…

In both directions (bidirectionally) from the origin

• Origins move to opposite ends of the cell

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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

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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

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Cytokinesis

occur after cell
division when two daughter
cells are created

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Septation

formation of
cross walls between
daughter cells

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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

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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

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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

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Exponential (log) phase

microbes are growing and
dividing at the → maximum rate possible
• Based on genetics, the medium used, and
environmental conditions

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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

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Possible reasons for stationary phase:

• Nutrient limitation
• Limited oxygen availability
• Toxic waste accumulation
• Critical population density reached

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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

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Viable but nonculturable (VBNC)

cell response to
starving, temporarily unable to grow
• Once conditions improve cells will begin to →grow
again

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Programmed cell death

part of the microbial population
is genetically programmed to die after growth stops
• Sacrificing themselves to benefit the population

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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

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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

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Hypotonic solution

(lower osmotic concentration)
• Water enters the cell
• Cell swells and may burst (plasmoptysis)

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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

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?

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