chp 7 microbial growth

Question 1

What are the differences between the reproductive strategies of eukaryotic and prokaryotic microbes?

Answer 1

Eukaryotic Microbes: Haploid or Diploid, Asexual and Sexual
Prokaryotic: Haploid only, asexual (binary fission, budding, filamentous), all must replicate and segregate the genome prior to division

Question 2

What are the two steps of the bacterial cell cycle?

Answer 2

(1) DNA replication and partition, (2) cytokinesis

Question 3

Explain the process of chromosome replication and partitioning:

Answer 3

Origin of replication (ori): 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 from origin  origins move to opposite ends of the cell

Question 4

Name the “key players” in the chromosome and partitioning process and what each of their functions are:

Answer 4

Replisome pushes/leads to condensation of daughter chromosomes to opposite ends

Question 5

Explain chromosome partitioning in C. cresentus

Answer 5

ParA polymerizes to form filaments  ParB binds to DNA at parS site near origin of replication  ParB binds 2 copies of parS site since DNA has been replicated, ParA interacts with one of the two ParB/parS complexes  depolymerization of ParA  pulls one copy of the DNA away system is almost 70% of 400 sequences bacterial genomes

Question 6

Explain septation (definition and process):

Answer 6

Septation: is the formation of cross walls between daughter cells
1. selection of site for septum formation  2. Assembly of Z ring (composed of protein FtZ)  3. Assembly of cell wall synthesizing machinery  4. Constriction of cell and septum formation

Question 7

What does the Z Ring have to do with this process? How is it formed?

Answer 7

FtZ, tubulin homologue is found in most bacteria and archaea  Polymerization forms Z ring (filaments of meshwork)  MinCDE system in E.coli limits Z ring to cell center, MinC, MinD, MinE ossciallitae from one side of cell to other, high concentration of MinC at poles prevents formation of Z ring at those locations

Question 8

How is the divisome formed?

Answer 8

Anchoring proteins link Z ring ring to the plasma membrane (FtsA and ZipA)  cell wall synthesizing machinery assembled  constriction of the Z ring, invagination of the plasma membrane and synthesis of septal wall complete division

Question 9

Explain the process of cellular growth

Answer 9

Cell growth is determined by peptidoglycan synthesis in bacteria

a. What breaks down the cell wall? Penicillin binding proteins (PBPs) link peptidoglycan strands or catalyze controlled degradation for new growth
b. What builds up the cell wall? Autolysins carry out limited digestion of peptidoglycan, this activity allows new material to be added to the wall and division to occur, inhibition of peptidoglycan synthesis can weaken cell wall and lead to lysis
c. Why is this happening? Commonly used antibiotics inhibit cell wall formation (penicillin, vancomycin, bacitracin)

Question 10

What determines the shape of the cell for cocci? How so?

Answer 10

? Cocci divisome: new peptidoglycan forms only at septum, FtsZ determines site of cell growth

Question 11

What determines the shape of the cell for rods? How so?

Answer 11

MreB determines cell diameter/elongation as Z ring froms

Question 12

What determines the shape of the cell for vibrios?

Answer 12

FtsZ forms Z ring  MreB helical polymerization throughout cell  CreS (Crescentin) localizes to short, curved side of cell, assymetric cell wall synthesis forms curve

Question 13

What is growth?

Answer 13

Growth increases in cellular constituents that may result in increases in cell number and increases in cell size, refers to population growth rather than individual growth

Question 14

BE FAMILIAR WITH THE GROWTH CURVE!!!

a. When is it observed?b. What are the 5 phases?

Answer 14

When microorganisms are cultivated in batch culture

Lag, Log/Exponential, Stationary, Death, Long-term Stationary

Question 15

Lag phasde

Answer 15

phase at the beginning of the growth curve where nothing really happens

Question 16

log/exponenetial phase

Answer 16

incredible amount of growth in a short period of time

Question 17

stationary phase

Answer 17

decrease in nutrients, and increase in waste cell just maintain

Question 18

death phase

Answer 18

last phase, results in death of bacteria

Question 19

long term stationary phase

Answer 19

Can lasts months to years  Bacterial population evolves  natural selection is happening  This phase is a highly dynamic period  ‘birth’ and ‘death’ rates are balanced  Long-term batch cultures have an apparent carrying capacity that can only support a certain number of cells  Cells may show growth advantage in stationary-phase (GASP) phenotype

Question 20

Explain biphasic growth:

Answer 20

Stationary culture cells are inoculated into a medium containing both glucose and lactose. Growth first on most rapidly metabolized carbon source  then lag before growth on lactose (two extra enzyme needed from lac operon; lactase permease to bring in lactose and -galactosidase to break lactose down to galactose and glucose  f inoculate cells growing exponentially on glucose are placed into lactose, lag is seen

Question 21

What does it mean for a bacteria to be VBNC?

Answer 21

VBNC are bacteria that are alive but not growing or dividing on/in the routinely used bacteriological media, many bacteria (>60 species including a large number of human pathogens) are known to enter the VBNC state in response to natural stresses such as starvation and fluctuation in temperature or osmotic concentration (includes Escherichia coli, Vibrio cholerae and Listeria monocytogenes)

Question 22

How is VBNC different from dead cells?

Answer 22

Difference from a dead cell includes an intact membrane containing undamaged genetic information

Question 23

How is VBNC different from living cells?

Answer 23

Differences from a living cell includes cellular morphology, cell wall and membrane composition, metabolism, gene expression, physical and chemical resistances, adhesion properties and virulence potential

Question 24

What is an extremophile? Explain the environment each lives in.

Answer 24

Extremophiles: grow under harsh conditions that would kill most other organisms

Question 25

Halophiles

Answer 25

grow optimally in the presence of NaCl or other salts at a concentration above 0.2M

Question 26

Extreme halophiles

Answer 26

require salt concentrations of 2M and 6.2M, extremely high concentrations of potassium (K), cell wall, proteins, and plasma membrane require high salt to maintain stability and activity, includes the archaeal genus Halobacterium (collect K+ and Cl-)

Question 27

Acidophiles

Answer 27

growth optimum between pH 0-5.5

Question 28

Neutrophiles

Answer 28

growth optimum between pH 5.5-7

Question 29

Alkaliphiles (alkalophiles

Answer 29

growth optimum between pH 8.5-11.5

Question 30

Psychrophiles

Answer 30

0°C to 20°C, Isolated from marine sediments, sea ice, Antarctica, Adaptations include changes in protein structure, more α-helix, less -sheet, more polar, less hydrophobic amino acids, More unsaturated and shorter fatty acids in the cell membrane, Many accumulate compatible solutes to decrease the cytosol’s freezing point

Question 31

Psychotolerant

Answer 31

0°C to 35°C

Question 32

Mesophiles

Answer 32

20°C to 45°C

Question 33

Thermophiles

Answer 33

55°C to 85°C

Question 34

Hyperthermophiles

Answer 34

85°C to 113°C, Most are certain species of Archaea, enzymes and proteins are more heat stable, cytoplasmic membrane stable; monolayers and ether linkages, Bacteria’s cell membrane is more saturated, branched and higher molecular weight lipids, Protein structure stabilized by more H bonds, more proline, presence of chaperones

Question 35

Barotolerant

Answer 35

adversely affected by increased pressure, but not as severely as nontolerant organisms

Question 36

Barophilic / Piezophilic

Answer 36

require or grow more rapidly in the presence of increased pressure, change membrane fatty acids to adapt to high pressures, increase in unsaturated fatty acids as the pressure increases

Question 37

Explain water activity

Answer 37

Water activity (aw) of a solution is 1/100 the relative humidity of solution, also equal to ratio of solution’s vapor pressure (Psoln) to that of pure water (Pwater), low water activity means most water is bound, most microorganisms grow better at or higher than 0.98

Question 38

Obligate aerobe

Answer 38

grows in presence of atmospheric oxygen (O2); requires O2

Question 39

Facultative anaerobes

Answer 39

do not require O2 but grow better in its presence

Question 40

Aerotolerant anaerobes

Answer 40

grow with or without O2

Question 41

Obligate anaerobe

Answer 41

are usually killed in the presence of O2

Question 42

Microaerophile

Answer 42

requires 2–10% O2

Question 43

What are reactive oxygen species? How do organisms protect themselves against them?

Answer 43

superoxide radical (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (OH•), Aerobes produce protective enzymes: superoxide dismutase (SOD), catalase, peroxidase

Question 44

What is the effect of ionizing radiation? Why?

Answer 44

Mutations  death (sterilization). Because it disrupts chemical structure of many molecules, including DNA (damage may be repaired by DNA repair mechanisms if small dose)

Question 45

Deinococcus radiodurans

Answer 45

extremely resistant to DNA damage, “has been listed as the world’s toughest bacterium in The Guinness Book Of World Records”

Question 46

What is the effect of ultraviolet radiation? Why?

Answer 46

wavelength most effectively absorbed by DNA is 260 nm, mutations  death, causes formation of thymine dimers in DNA, DNA damage can be repaired by several repair mechanisms

Question 47

What is the effect of visible light?

Answer 47

at high intensities generates singlet oxygen (1O2)  powerful oxidizing agent

Question 48

Carotenoid pigments

Answer 48

protect many light-exposed microorganisms from photooxidation

Question 49

Define heterogeneity

Answer 49

is differences in metabolic activity and locations of microbes

Question 50

Define quorum sensing

Answer 50

bacterial cells in biofilms communicate in a density-dependent manner

Question 51

Symbiosis example

Answer 51

Vibrio fischeri and bioluminescence in a squid

Question 52

Pathogenicity (increased virulence factor production) example

Answer 52

Pseudomonas aeruginosa

Question 53

Competence (for antibiotic resistance) example

Answer 53

Bacillus subtilis

Question 54

Interdomain communication

Answer 54

Rhizobium interactions with leguminous plants for nitrogen fixation