Lecture 3 PMB

Question	Answer
balanced 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)
rich/complex medium	not chemically defined, contains complex organic molecules; wide variety of nutrients supplied by peptone, yeast extract, blood serum, etc
defined/minimal medium	composed of precise amounts of known chemicals; may or may not contain organic compounds
biosynthetic/metabolic capacity	= 1/Nutritional Requirements
exponential 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)
batch culture	CLOSED system where bacterial growth depletes nutrients + alters environment will see: lag --> exponential --> stationary--> death
stationary phase	microbial 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
cross-protection	when 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
Lag Phase	Occurs: (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
chemostat	open system for continuous microbial culture; cells are maintained in chemically constant environment Fresh medium added at top, but effluent contains both medium AND cells!
What happens if you increase the starting nutrient concentration in a series of otherwise identical batch cultures?	--> yield at stationary phase increases
effects of nutrient concentration on batch culture growth	the 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
dilution rate vs growth rate of bacteria in a chemostat	Dilution 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
heterotrophs	require an organic C source
autotrophs	get all of the C they need to build cell structures from CO2 in the air; perform carbon fixation!
nitrogen fixing bacteria	convert atmospheric N2 to NH4+, assimilate it into cellular structures/share with other organisms
Obligate aerobes	MUST use O2 as terminal e- acceptor in respiration most growth adjacent to air
obligate anaerobes	MUST avoid O2, or key enzymes will be harmed and they will die Gain energy by anaerobic respiration or fermentation; grow away from air
Facultative anaerobes	can 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
Microaerophiles	live 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
Aerotolerant anaerobes	neither 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
Whats 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)
What do bacteria do to handle oxygen?	2 H2O2 + CATALASE --> 2H2O + O2 NADH + 2 H2O2 + PEROXIDASE --> 2 H2O + NAD+
(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
(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)
Psychrophile solutions to proteins performing reactions more slowly	(1) Individual proteins more flexible than for mesophilic or thermophilic bacteria
Psychrophile 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)
Psychrophile 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!)
bacterial adaptations to hypotonic conditions	hypotonic 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
bacterial 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+)

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	Created by Candice Young over 6 years ago