chp 7 microbial growth Flashcards
What are the differences between the reproductive strategies of eukaryotic and prokaryotic microbes?
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
What are the two steps of the bacterial cell cycle?
(1) DNA replication and partition, (2) cytokinesis
Explain the process of chromosome replication and partitioning:
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
Name the “key players” in the chromosome and partitioning process and what each of their functions are:
Replisome pushes/leads to condensation of daughter chromosomes to opposite ends
Explain chromosome partitioning in C. cresentus
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
Explain septation (definition and process):
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
What does the Z Ring have to do with this process? How is it formed?
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
How is the divisome formed?
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
Explain the process of cellular growth
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)
What determines the shape of the cell for cocci? How so?
? Cocci divisome: new peptidoglycan forms only at septum, FtsZ determines site of cell growth
What determines the shape of the cell for rods? How so?
MreB determines cell diameter/elongation as Z ring froms
What determines the shape of the cell for vibrios?
FtsZ forms Z ring MreB helical polymerization throughout cell CreS (Crescentin) localizes to short, curved side of cell, assymetric cell wall synthesis forms curve
What is growth?
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
BE FAMILIAR WITH THE GROWTH CURVE!!!
a. When is it observed?b. What are the 5 phases?
When microorganisms are cultivated in batch culture
Lag, Log/Exponential, Stationary, Death, Long-term Stationary
Lag phasde
phase at the beginning of the growth curve where nothing really happens
log/exponenetial phase
incredible amount of growth in a short period of time
stationary phase
decrease in nutrients, and increase in waste cell just maintain
death phase
last phase, results in death of bacteria
long term stationary phase
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
Explain biphasic growth:
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
What does it mean for a bacteria to be VBNC?
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)
How is VBNC different from dead cells?
Difference from a dead cell includes an intact membrane containing undamaged genetic information
How is VBNC different from living cells?
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
What is an extremophile? Explain the environment each lives in.
Extremophiles: grow under harsh conditions that would kill most other organisms
Halophiles
grow optimally in the presence of NaCl or other salts at a concentration above 0.2M
Extreme halophiles
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-)
Acidophiles
growth optimum between pH 0-5.5
Neutrophiles
growth optimum between pH 5.5-7
Alkaliphiles (alkalophiles
growth optimum between pH 8.5-11.5
Psychrophiles
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
Psychotolerant
0°C to 35°C
Mesophiles
20°C to 45°C
Thermophiles
55°C to 85°C
Hyperthermophiles
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
Barotolerant
adversely affected by increased pressure, but not as severely as nontolerant organisms
Barophilic / Piezophilic
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
Explain water activity
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
Obligate aerobe
grows in presence of atmospheric oxygen (O2); requires O2
Facultative anaerobes
do not require O2 but grow better in its presence
Aerotolerant anaerobes
grow with or without O2
Obligate anaerobe
are usually killed in the presence of O2
Microaerophile
requires 2–10% O2
What are reactive oxygen species? How do organisms protect themselves against them?
superoxide radical (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (OH•), Aerobes produce protective enzymes: superoxide dismutase (SOD), catalase, peroxidase
What is the effect of ionizing radiation? Why?
Mutations death (sterilization). Because it disrupts chemical structure of many molecules, including DNA (damage may be repaired by DNA repair mechanisms if small dose)
Deinococcus radiodurans
extremely resistant to DNA damage, “has been listed as the world’s toughest bacterium in The Guinness Book Of World Records”
What is the effect of ultraviolet radiation? Why?
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
What is the effect of visible light?
at high intensities generates singlet oxygen (1O2) powerful oxidizing agent
Carotenoid pigments
protect many light-exposed microorganisms from photooxidation
Define heterogeneity
is differences in metabolic activity and locations of microbes
Define quorum sensing
bacterial cells in biofilms communicate in a density-dependent manner
Symbiosis example
Vibrio fischeri and bioluminescence in a squid
Pathogenicity (increased virulence factor production) example
Pseudomonas aeruginosa
Competence (for antibiotic resistance) example
Bacillus subtilis
Interdomain communication
Rhizobium interactions with leguminous plants for nitrogen fixation
