topic 5: chemical and environmental influence on microbial growth Flashcards
what are the 5 environmental influences on microbial growth
- Temperature
- Pressure
- Osmolarity
- pH
- Oxygen
how does temperature affect growth rates of enzymes?
high temperatures: growth rates decrease because enzymes denature
low temperatures: growth rates decrease because of decrease in membrane fluidity and enzymatic activity
what are psychrophiles
-produce enzymes that function optimally at cold temperatures
-cytoplasmic membrane has higher concentration of unsaturated fatty acids to maintain membrane fluidity (pack less tightly to allow for fluidity at cold temps)
what are thermophile and hyperthermophiles
-stable enzymes/proteins that resist unfolding (denaturation) at high temps
-cytoplasmic membrane rich in saturated fatty acids
what are barophiles
-requires high pressure to grow
-most are also psychrophiles
what are barotolerant
organisms grow up to a certain pressure, die at high pressures
barosensitive
organisms die as pressure increases
how do non-halophiles avoid lethal effects of extreme osmotic stress in hypertonic and hypotonic conditions
hypertonic:
stop import and synthesis of compatible solutes, mechanosensitive membrane channels open allowing solutes to diffuse out of cytoplasm
hypotonic:
stop import and synthesis of compatible solutes, maintain high concentration of inorganic or organic solutes in the cytoplasm
what are extreme halophiles
-distinct group of archaea
-requirement for high [NaCl]
-adaptation through K+ import
-proteins have more Asp and Glu amino acids on surface, the carboxylic acids interact with K+ which attracts water to keep protein hydrated
how does pH affect enzymes in acidic and alkaline environments
-enzymes have optimum activity at particular pH
-environmental pH affects proton motif force and therefore energy generation
-microbes maintain internal cytoplasm at neutral pH
acidic: cytoplasm risks becoming acidic (protons move into cytoplasm), pumps protons out or produce enzymes that catalyze reactions that consume protons
alkaline: cytoplasm risks becoming alkaline (protons move out of cytoplasm), microbes pump protons into cells or produce enzymes that catalyze the production of acids
what is an obligate anaerobe?
cannot come in contact with oxygen
what is an obligate aerobe?
grows at bottom, cannot be in contact with oxygen
what is a microaerophile?
requires small amount of oxygen, grows in middle
what is a facultative anaerobe?
grows anywhere in column, grows with or without oxygen
what is oxygen required for and how are oxygen radicals detoxified
What is oxygen required for?
§ In the electron transport chain during oxidative phosphorylation, oxygen is the final electron acceptor
§ Radical formation due to incomplete reduction of oxygen gas
Strategies to detoxify oxygen radicals
-Enzyme superoxide dismutase
-Enzymes catalase
-Enzyme peroxidas
methods to control microbial growth
a) physical (heat, radiation, filtration)
b) chemical (biocides/disinfectants, antibiotics)
-for external use
-for in-vivo use
physical methods of controlling microbial growth-heat
Moist heat
-use of steam (work by denaturing proteins, unfolds and sticks to other protein)
-Steam can kill bacterial endospores in a short period of time
Pasteurization
-kill bacteria in milk that cause diseases
-Reduces number of microorganisms, prevents spoilage for a certain period of time
Dry heat
-Kills by oxidation
Ex: inoculating loop in Bunsen burner
physical methods of controlling microbial growth-radiation
Ultraviolet light-damage DNA
-Ionizing radiation (x-rays, gamma rays) damage DNA and proteins
-Bacteria is generally much more resistant to ionizing radiation than human
physical methods of controlling microbial growth-filtration
-Membranes with 0.2 micrometre pore size
-Syringe filter or vacuum used to pull
chemical methods of controlling microbial growth- biocides/disinfectants
- oxidizers
- membrane disruptors
- protein denaturants
how do antibiotics work (general)
-targets specific cellular structures, usually specific to certain types of bacteria
-used to treat disease/infections in humans and animals
mechanisms of antibiotics
A) Inhibit cell wall synthesis
B) Inhibit protein synthesis
C) Affect nucleic acid synthesis or integrity
D) Disrupt cell membrane
E) Inhibit synthesis of an essential metabolite
inhibit cell wall synthesis- penicillin
-penicillin binding protein (PBP) catalyze transpeptidase reaction for peptidoglycan
-penicillin inhibits peptidoglycan synthesis by inhibiting PBP
-disrupts peptidoglycan cell wall strength, leads to unrestrained osmosis and cell lysis
enzyme inhibitors
competitive: binds to active site iteself
non-competitive: binds to allosteric site, alters active site
inhibit cell wall synthesis- vancomycin
-inhibits transpeptidation (works differently than penicillin)
-binds to D-ala-D-ala on NAM, preventing this rxn
-does not bind to PBP, binds to the substrate of PBP
inhibit protein synthesis
-inhibits ribosomes by binding and preventing protein synthesis
-antibiotics
○ Streptomycin
○ Tetracycline
○ Chloramphenicol
○ Erythromycin
affect nucleic acid synthesis and integrity-quinolones
DNA gyrase catalyze DNA supercoiling
○ Quinolones bind to DNA gyrase
○ Causes gyrase-DNA covalent complex to be stuck at this stage
○ Prevents DNA polymerase from accessing origin of replication
affect nucleic acid synthesis and integrity-metronidazole
· Free radical form of metronidazole causes DNA breaks
○ Anaerobic bacteria donates electrons to prodrug forming the radical form of metronidazole that causes DNA breaks
○ Kills anaerobic bacteria
○Usually prescribed for dental cavitie
affect nucleic acid synthesis and integrity-rifampin
Binds to RNA polymerase and inhibits transcription of genes (DNA to RNA)
affect nucleic acid synthesis and integrity-actinomycin D
-Binds to DNA
-DNA polymerase, RNA polymerase and other DNA binding proteins cannot access DNA thereby interfere with replication and transcription process, it is a peptide antibiotic
disrupt cell membrane
-Gramicidin forms a channel through the cytoplasmic membrane allowing free diffusion of cations
-Antibiotic more effective on gram positive bacteria
inhibit synthesis of an essential metabolite
-PABA required for synthesis of folic acid, and is an essential vitamin
-Sulfanilamide binds to enzyme required for folic acid synthesis from PABA-inhibits activity
antibiotic resistance mechanisms
- Bacteria produces enzymes that modifies antibiotic, making it ineffective in inhibiting enzyme function
· Ex: B-lactamase changes chape of penicillin, cannot bind - Mutation of gene that encodes the antibiotic target
· Single amino acid change in bacterial ribosome may be sufficient to prevent macrolide antibiotic from disrupting its function - Preventing antibiotics from penetrating bacteria cells or actively pumping antibiotics out of the cell
· ArcAB utilizes the proton motif force to pump antibiotics out of the cell through TolC
Why are slow growing bacteria (ex: Mycobacterium tuberculosis) generally more resistant to antibiotics?
-Has thick outer membrane that doesn’t allow antibiotics in as easily
-Bacteria must build cell wall when it divides, when it grows slowly, it is not dividing or actively making more proteins, making it harder to target since antibiotics target cell division to attack
