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Lecture 3 PMB
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- 1balanced growth--> when bacteria have enough of all required nutrients to duplicate into cellular structures and divide
--> an increase in cell mass due to having DNA, RNA, protein, cell wall material (NOT due to having storage material) - 2rich/complex mediumnot chemically defined, contains
complex organic molecules; wide variety of nutrients supplied by peptone, yeast extract, blood serum, etc - 3defined/minimal mediumcomposed of precise amounts of known chemicals; may or may not contain organic compounds
- 4biosynthetic/metabolic capacity= 1/Nutritional Requirements
- 5exponential growth--> occurs when a bacterial population has sufficient nutrients + is
not limited by its environment
--> # of cells in pop and total cell mass increase by factor of 2 during each
generation time
--> N = N0 x 2^n
(N0 = initial cell #, n = # of generations)
--> g = t/n
(t = exponential growth time) - 6batch cultureCLOSED system where bacterial growth depletes nutrients + alters environment
will see: lag --> exponential --> stationary--> death - 7stationary phasemicrobial growth limited because:
cells run out of essential nutrient and/or accumulate toxic waste product
--> NO net increase/decrease in cell #, metabolism + some biosynthetic processes can continue (DNA/protein ratio increases)
--> might see change in morphology
--> no longer balanced growth!
--> in nature this is usually what we see - 8cross-protectionwhen starved cells become resistant to a wide variety of stresses (heat, oxidants, and osmosis) and produce proteins to protect them
--> sigma S turns on genes for this
--> we see this during stationary phase - 9Lag PhaseOccurs: (1) when stationary-phase culture diluted into fresh medium OR (2) cells transferred from rich --> minimal medium
Bacteria sense new environment and synthesize: (1) proteins needed for rapid growth (not produced during starvation) OR (2) specific proteins needed to produce nutrients not already present in medium - 10chemostatopen system for continuous microbial culture; cells are maintained in chemically constant environment
Fresh medium added at top, but effluent contains both medium AND cells! - 11What happens if you increase the starting nutrient concentration in a series of otherwise identical batch cultures?--> yield at stationary phase increases
- 12effects of nutrient concentration on batch culture growththe lower the nutrient concentration, the higher the maximal growth rate during exponential phase
once nutrient conc. reaches a minimum level, bacteria grow at average max rate
-->if culture starts using higher conc. of nutrients --> yield increases, BUT growth rate during exponential phase still constant
TLDR: yield constantly increases with nutrient conc. but growth rate only increases until some minimum level - 13dilution rate vs growth rate of bacteria in a chemostatDilution rate (DR) = fraction culture volume replaced per [unit time] by fresh medium
DR too fast: cell division can’t keep up, culture washes out
DR too slow: cells will starve b/c limiting nutrient isn’t being supplied fast enough
increase DR --> doubling time decreases, near-optimal conditions until wash-out - 14heterotrophsrequire an organic C source
- 15autotrophsget all of the C they need to build cell structures from CO2 in the air; perform carbon fixation!
- 16nitrogen fixing bacteriaconvert atmospheric N2 to NH4+, assimilate it into cellular structures/share with other organisms
- 17Obligate aerobesMUST use O2 as terminal e- acceptor in respiration
most growth adjacent to air - 18obligate anaerobesMUST avoid O2, or key enzymes will be harmed and they will die
Gain energy by anaerobic respiration or fermentation; grow away from air - 19Facultative anaerobescan either use O2 in respiration or use fermentation/etc when no O2 is available; grow faster when O2 is present
grow everywhere but mostly by air interface - 20Microaerophileslive ONLY in places where the O2 concentration is low (not high or zero)
contain some enzyme easily damaged by oxygen; grow right below air interface - 21Aerotolerant anaerobesneither use O2 for respiration nor are harmed by it; don’t grow any faster or slower if O2 is present
only ferment or use non-oxygen electron acceptors; grow anywhere without caring - 22Whats the matter with oxygen?When oxygen is present, electron-carrying molecules can donate electrons to it (by accident) to create reactive oxygen species
ROS can react w/ nucleic acids, proteins, and lipids to cause cell damage
includes: superoxide radical (oxidation of FAD), hydrogen peroxide, hydroxyl radical (Fenton reaction) - 23What do bacteria do to handle oxygen?2 H2O2 + CATALASE --> 2H2O + O2
NADH + 2 H2O2 + PEROXIDASE --> 2 H2O + NAD+ - 24(Hyper)thermophile solutions to critical enzymes denaturing in heat(1) individual proteins have fewer glycines or have increased ionic bonding between polar amino acids and hydrophobic cores
(2) chaperones refold denatured proteins
(3) solutes (di-inositol phosphate, diglycerol phosphate) help stabilize proteins - 25(Hyper)thermophile solutions to membrane being to fluid/losing its ability as a barrier(1) synthesize phospholipids with SATURATED fatty acids (linear and pack tightly against each other --> form an organized, heat-resistant membrane)
- 26Psychrophile solutions to proteins performing reactions more slowly(1) Individual proteins more flexible than for mesophilic or thermophilic bacteria
- 27Psychrophile solutions to membrane fluidity decreasing (inhibiting function of transmembrane proteins)(1) Membrane phospholipids have more UNSATURATED fatty acids + more short-chain fatty acids (do not pack tightly and remain mobile even at cold temperatures)
- 28Psychrophile solutions to ice crystals forming in cytoplasm and puncturing cell wall(1) produce cryoprotectants (glycerol, sugars) at high concentrations that prevent ice crystal formation (antifreeze!)
- 29bacterial adaptations to hypotonic conditionshypotonic medium --> water rushes in to make cell more dilute --> cell lysis
SOLUTIONS
(1) rigid cell walls that withstand internal pressure and prevent osmotic lysis
(2) mechanosensitive channels activated by high internal pressures --> can leak solutes out of the cell to reduce internal osmolarity - 30bacterial adaptations to hypertonic solutions (ie. halophiles)hypertonic medium --> water rushes out of cell --> enzyme function/cell growth halted
SOLUTIONS
(1) synthesize/import compatible solutes: small molecules/ions that do not disrupt cell metabolism BUT increase internal osmolarity (includes proline, glutamic acid, glycerol, and K+)