Microbacterial Growth and Reproduction

What are the reproductive strategies of eukaryotic microbes?

asexual and sexual, haploid or diploid

What are the reproductive strategies of bacteria and archaea?

haploid only, asexual binary fission, budding, filamentous

must replicate and segregate the genome prior to division

What is the cell cycle?

a sequence of events from formation of new cell through the next cell division

How is most bacteria divided by?

binary fission

What are the two pathways function during cycle?

DNA replication and partition, cytokinesis

What shape are most bacterial chromosomes?

circular

What is the origin of replication?

site at which replication begins

What is the terminus?

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

What is a replisome?

group of proteins needed for DNA synthesis

Which direction does DNA replication proceed from the origin?

both directions

What does replisome do?

pushes, or condensation of, daughter chromosomes to opposite ends

What is MreB (murein cluster B)?

an actin homolog, plays role in determination of cell shape as spiral inside cell periphery, and chromosome segregation

What happens if MreB is mutated?

chromosomes do not segregate

What is septation?

formation of cross walls between daughter cells

What are the steps of septation?

• selection of site for septum formation

• assembly of Z ring

• linkage of Z ring to plasma membrane (cell wall)

• assembly of cell wall synthesizing machinery

• constriction of cell and septum formation

What does Z ring do?

constricts and forms septum

What is polymerization?

multiple proteins bind together

What is protein FtsZ?

tubulin homologue, found in most bacteria and archaea, polymerization forms Z ring, filaments of meshwork

What limits the z ring to the center of the cell in E. coli?

MinCDE

What does MinCDE do?

oscillates from one side of cell together, link Z ring to cell membrane, Z ring constricts and cell wall synthesis of septal wall

What determines cellular growth and cell shape?

peptidoglycan synthesis in bbacteria

What do penicillin binding proteins (PBPs) do?

link peptidoglycan strands and catalyze controlled degradation for new growth

What are autolysins?

PBP enzymes that degrade peptidoglycan and site new units added

What carries NAM-UDP NAG unit across cytoplasmic membrane?

bactoprenol

What is cocci divisome?

new peptidoglycan forms only at the central septum

What does FtsZ do?

it determines the site of cell wall growth and may recruit PBPs for synthesis of septum

When do rods elongate?

prior to seperation

What does MreB do?

it determines cell diameter and elongates as Z ring forms in center

Increases in cellular constituents that may result in:

• increase in cell number

• increase in cell size

What does growth mean?

it refers to population growth

What does growth not mean?

growth of individual cells

When is the growth curve observed?

when microorganisms are cultivated in batch culture

How is the growth curve culture incubated?

in a closed vessel with a single batch of medium

How is the growth curve plotted?

as a logarithm of a cell number versus time

What are the phases of the growth curve?

lag, exponential (log), stationary, death (sequence)

What is happening in the lag phase?

cell synthesizing new components

Why do the cells synthesize new components?

to replenish spent materials and to adapt to new medium or other conditions

How long is the lag phase?

it varies in length (in some cases can be very short or even absent)

What happens in the exponential (log) phase?

the rate of growth and division is constant and maximal

What phase is population most uniform in terms of chemical and physical properties?

exponential (log) phase

When do cells exhibit balanced growth?

exponential (log) phase

What is balanced growth?

cellular constituents manufactured at constant rates relative to each other

What is unbalanced growth?

rates of synthesis of cell components vary relative to each other

What conditions does unbalanced growth occur under?

change in nutrient levels or change in environmental conditions (temp, pH, etc.)

What is happening in the stationary phase?

active cells stop reproducing or reproductive rate is balanced by death rate (total number of variable cells remains constant)

What are some possible reasons for stationary phase?

• nutrient limitation

• limited oxygen availability

• toxic waste accumulated

• critical population density reached

How do you prevent limited oxygen availability in the stationary phase?

could be placed on a shaker

What causes entry into the stationary phase?

starvation and other stressful conditions activating survival strategy

What are the survival strategies of cells in the stationary phase?

• morphological changed (endospore formation)

• decrease in size, protoplast shrinkage, and nucleoid condensation

• RpoS protein assists RNA polymerase in transcribing genes for starvation proteins

What does the production of starvation proteins do?

• increase cross-linking. in cell wall

• Dps protein protects DNA

• chaperone proteins prevent protein damage

What do chaperone proteins do?

help maintain cell shape and function

What are persister cells?

cells that have long term survival and increased virulence

What are the two hypotheses of the senescence and death phase?

cells are viable but not culturable (VBNC) and programed cell death

What does it mean that cells are viable but not culturable (VBNC)?

cells alive, but dormant, capable of new growth when conditions are right

What does it mean that cells get programed death?

fraction of the population genetically programed to die (cell suicide)

What phase is generation time determined in?

log phase

What are two ways to measure microbial growth?

can measure changes in number of cells in population and can measure changes in mass of population

What are direct cell count methods?

counting chambers, electronic counters (flow cytometry), and on membrane filters

What are advantages of counting chambers?

it is easy, inexpensive, and quick. its usefulf or counting eukaryotes and prokaryotes

What are disadvantages to counting chambers?

cannot distinguish living from dead cells

What are the advantages of on membrane filters?

it can distinguish living from dead cells with certain dyes

What are the advantages of flow cytometry?

specific antibodies can be used to determine size and internal complexity

What are disadvantages of spread and pour plate techniques?

dilutions are a pain and takes a lot of time

What are counting chambers?

grid to look at under microscope to count cells

What are on membrane filters?

cells filtered through special membrane that provides dark background for observing cells

What is flow cytometry?

microbial suspension forced through small orifice with a laser light beam

What are viable counting methods?

• spread and pour plate

• membrane filter

How do you measure cell mass?

• dry weight

• quantity of a particular cell constituent

  • turbidimetric measures (light scattering)

What are the disadvantages of dry weight?

time consuming and not very sensitive

In what circumstances is quantity of a particular cell constituent useful?

if the amount of substance in each cell is constant (protein, DNA, ATP, chlorophyll)

What are the benefits of turbidometric method?

it is quick, easy, and sensitive

What is the continuous culture of microorganisms?

it is growth in an open system, it maintains cells in a log phase

What does growth in an open system require?

continual provision of nutrients and continual removal of wastes

What is the importance of continuous culture methods?

• constant supply of cells in exponential phase growing at a known rate

• study of microbial growth at very low nutrient concentrations, close to those present in natural environment

• study of interactions of microbes under conditions resembling those in aquatic environments

• food and industrial microbiology

On a chemostat, what is the rate of incoming medium equal to?

rate of removal if medium from vessel

What kind of conditions do most organisms grow in?

fairly moderate environmental conditions (O₂, pH, temp, etc.)

What is an extremophile?

organism that grows under harsh conditions that would kill most other organisms

What does halotolerant / osmotolerant mean?

able to grow over wide ranges of water activity or osmotic concentration

What does halophile mean?

requires high levels of sodium chloride, usually above about 0.2 M, to grow

What does acidophile mean?

growth optimum between pH of 0-5.5

What does neutrophile mean?

growth optimum between pH 5.5-8W

What does alkalophile mean?

growth optimum between 8-11.5

What does psycrophile mean?

growth at 0°C and has an optimum growth temperature of 15°C or lower

What does psycrotolerant mean?

can grow at 0-7°C; has an optimum between 20 and 30°C and a maximum around 35°C

What does mesophile mean?

has optimum between 20-45°C

What does thermophile mean?

can grow at 55°C or higher; optimum often between 55 and 65°C

What is a hyperthermophile?

has optimum between 85 and about 113°C

What does obligate aerobe mean?

completely dependent on atmospheric O₂ for growthWh

What does facultative anaerobe mean?

does not require O₂ for growth but grows better in its presence

What does aerotolerant anaerobe mean?

grows equally well in presence or absence of O₂

What does obligate anaerobe mean?

does not tolerate O₂ and dies in its presence

What does microaerophile mean?

requires O₂ levels between 2-10% for growth and is damaged by atmospheric O₂ levels (20%)

What does barophile mean?

growth more rapid at high hydrostatic pressures

What is a hypertonic solution?

lower osmotic concentration

What happens in a hypotonic solution?

water enters the cell and cell swells may burst

What is a hypertonic solution?

higher osmotic concentration

What happens in a hypertonic solution?

water leaves the cell and membrane shrinks from the cell wall (plasmolysis) may occur

How do microbes adapt to changes in osmotic ocncentrations?

they reduce osmotic concentration of cytoplasm in hypotonic solutions and increase internal solute concentration with their compatible solutes

How can cells reduce their osmotic concentration of cytoplasm in hypotonic solutions?

mechanosensitive (MS) channels in plasma membrane allow solutes to leave

Where are extreme halophiles found?

in salt mines