Created by Candice Young
over 6 years ago
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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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